diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+## 0.2
+
+* Allow add not only dependencies, but also modules.
+* Allow to rename dependencies and modules.
+
 ## 0.1
 
 * Initial release.
diff --git a/app/Main.hs b/app/Main.hs
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -12,15 +12,15 @@
 import Cabal.Project (parseProject, prjPackages, resolveProject)
 import Control.Exception (throwIO)
 import Control.Monad (filterM)
+import Data.Bifunctor (bimap)
 import Data.ByteString (ByteString)
 import Data.ByteString.Char8 qualified as B
 import Data.Either (partitionEithers)
 import Data.List qualified as L
 import Data.List.NonEmpty (NonEmpty (..))
-import Data.Maybe (catMaybes)
+import Data.Maybe (catMaybes, isJust)
 import Distribution.CabalSpecVersion (CabalSpecVersion)
 import Distribution.Client.Add
-import Distribution.Fields (Field)
 import Distribution.PackageDescription (
   ComponentName,
   GenericPackageDescription,
@@ -28,7 +28,6 @@
   specVersion,
  )
 import Distribution.PackageDescription.Quirks (patchQuirks)
-import Distribution.Parsec (Position)
 import Options.Applicative (
   Parser,
   execParser,
@@ -45,7 +44,7 @@
  )
 import Options.Applicative.NonEmpty (some1)
 import System.Directory (doesFileExist, listDirectory)
-import System.Environment (getArgs, withArgs)
+import System.Environment (getArgs, lookupEnv, withArgs)
 import System.Exit (die)
 import System.FilePath (takeDirectory, (</>))
 
@@ -128,23 +127,27 @@
 stripAdd ("add" : xs) = xs
 stripAdd xs = xs
 
-type Input =
-  ( FilePath
-  , ByteString
-  , [Field Position]
-  , GenericPackageDescription
-  , Either
-      CommonStanza
-      ComponentName
-  , NonEmpty ByteString
-  )
+data Input = Input
+  { inpFilePath :: FilePath
+  , inpPackageDescription :: GenericPackageDescription
+  , inpConfig :: AddConfig
+  }
+  deriving (Show)
 
 mkInputs
   :: Bool
+  -- ^ Must the first argument be a component name?
+  -- As opposed to interpreting it as one of dependencies to add.
   -> FilePath
+  -- ^ Cabal file name, primarily for error reporting.
+  -- Note that 'mkInputs' does not do any 'IO'.
   -> ByteString
+  -- ^ Cabal file content.
   -> NonEmpty String
+  -- ^ List of arguments. The first one is either a component name
+  -- or a dependency (see 'Bool' flag above), the rest are dependencies.
   -> Either String Input
+  -- ^ Either an error or a tuple of input data.
 mkInputs isCmpRequired cabalFile origContents args = do
   (fields, packDescr) <- parseCabalFile cabalFile origContents
   let specVer :: CabalSpecVersion
@@ -157,35 +160,48 @@
     x :| (y : ys)
       | Right c <- mkCmp (Just x) ->
           (c,) <$> mkDeps (y :| ys)
+      | isCmpRequired -> Left $ "Target component '" ++ x ++ "' is not found"
     _ ->
       if isCmpRequired
-        then Left "Component is required"
+        then Left "Target component is required"
         else (,) <$> mkCmp Nothing <*> mkDeps args
-  pure (cabalFile, origContents, fields, packDescr, cmp, deps)
+  pure $
+    Input
+      cabalFile
+      packDescr
+      AddConfig
+        { cnfOrigContents = origContents
+        , cnfFields = fields
+        , cnfComponent = cmp
+        , cnfTargetField = BuildDepends
+        , cnfAdditions = deps
+        }
 
 disambiguateInputs
   :: Maybe FilePath
-  -> [FilePath]
-  -> [Either a Input]
+  -> [(FilePath, Either String Input)]
   -> Either String Input
-disambiguateInputs mProjectFile cabalFiles inputs = case partitionEithers inputs of
+disambiguateInputs mProjectFile inputs = case inputs' of
   ([], []) -> Left $ case mProjectFile of
     Nothing -> "No Cabal files or projects are found in the current folder, please specify --project-file."
     Just projFn -> "No Cabal files are found in " ++ projFn
-  (_errs, []) ->
+  (errs, []) ->
     Left $
-      "No matching targets found amongst: "
-        ++ L.intercalate ", " cabalFiles
-  (_, [inp]) -> pure inp
+      L.intercalate "\n" $
+        map (\(fn, err) -> "Cannot add a dependency to " ++ fn ++ " because: " ++ err) errs
+  (_, [inp]) -> pure $ snd inp
   (_, _inps) ->
     Left
-      "Target component is ambiguous, please specify it as package:type:component. See https://cabal.readthedocs.io/en/latest/cabal-commands.html#target-forms for reference"
+      "Cannot add a dependency, because target component is ambiguous. Please specify it as package:type:component. See https://cabal.readthedocs.io/en/latest/cabal-commands.html#target-forms for reference"
+  where
+    inputs' = partitionEithers $ map (\(fn, e) -> bimap (fn,) (fn,) e) inputs
 
 main :: IO ()
 main = do
+  isCabalEnvVarSet <- isJust <$> lookupEnv "CABAL"
   rawArgs <- getArgs
   RawConfig {..} <-
-    withArgs (stripAdd rawArgs) $
+    withArgs ((if isCabalEnvVarSet then stripAdd else id) rawArgs) $
       execParser $
         info
           (helper <*> parseRawConfig)
@@ -196,14 +212,27 @@
     catMaybes
       <$> traverse (\fn -> fmap (fn,) <$> readCabalFile fn) cabalFiles
   let getInput isCmpRequired =
-        disambiguateInputs rcnfMProjectFile (fmap fst cabalFilesAndContent) $
-          map (\(fn, cnt) -> mkInputs isCmpRequired fn cnt rcnfArgs) cabalFilesAndContent
+        disambiguateInputs rcnfMProjectFile $
+          map
+            (\(fn, cnt) -> (fn, mkInputs isCmpRequired fn cnt rcnfArgs))
+            cabalFilesAndContent
 
-  input <- either (const $ either die pure $ getInput True) pure (getInput False)
+  input <- case getInput False of
+    Right i -> pure i
+    Left errFalse -> case rcnfArgs of
+      _ :| [] -> die errFalse
+      _ -> case getInput True of
+        Right i -> pure i
+        Left errTrue ->
+          die $
+            "If the first argument is interpreted as a dependency:\n"
+              ++ errFalse
+              ++ "\n\nIf the first argument is interpreted as a target component:\n"
+              ++ errTrue
 
-  let (cabalFile, cnfOrigContents, cnfFields, origPackDescr, cnfComponent, cnfDependencies) = input
+  let Input cabalFile origPackDescr cnf = input
 
-  case executeConfig (validateChanges origPackDescr) (Config {..}) of
+  case executeAddConfig (validateChanges origPackDescr) cnf of
     Nothing ->
       die $
         "Cannot extend build-depends in "
diff --git a/cabal-add.cabal b/cabal-add.cabal
--- a/cabal-add.cabal
+++ b/cabal-add.cabal
@@ -1,12 +1,12 @@
 cabal-version:   3.0
 name:            cabal-add
-version:         0.1
+version:         0.2
 license:         BSD-3-Clause
 license-file:    LICENSE
 maintainer:      andrew.lelechenko@gmail.com
 author:          Bodigrim
 tested-with:
-    ghc ==9.10.1 ghc ==9.8.2 ghc ==9.6.6 ghc ==9.4.8 ghc ==9.2.8
+    ghc ==9.12.2 ghc ==9.10.2 ghc ==9.8.4 ghc ==9.6.7 ghc ==9.4.8
 
 synopsis:        Extend Cabal build-depends from the command line
 description:
@@ -25,31 +25,23 @@
     type:     git
     location: https://github.com/Bodigrim/cabal-add.git
 
-flag cabal-syntax
-    default: False
-
 library
-    exposed-modules:  Distribution.Client.Add
+    exposed-modules:
+        Distribution.Client.Add
+        Distribution.Client.Rename
+
     hs-source-dirs:   src
+    other-modules:    Distribution.Client.Common
     default-language: GHC2021
     ghc-options:      -Wall
     build-depends:
         base <5,
         bytestring <0.13,
-        Cabal >=3.6 && <3.13,
-        containers <0.8,
+        Cabal >=3.8 && <3.15,
+        Cabal-syntax >=3.8 && <3.15,
+        containers <0.9,
         mtl <2.4
 
-    if flag(cabal-syntax)
-        build-depends:
-            Cabal-syntax >=3.8 && <3.13,
-            Cabal >=3.8
-
-    else
-        build-depends:
-            Cabal-syntax <3.7,
-            Cabal <3.7
-
 executable cabal-add
     main-is:          Main.hs
     hs-source-dirs:   app
@@ -60,17 +52,12 @@
         bytestring <0.13,
         cabal-add,
         cabal-install-parsers >=0.4.1 && <0.7,
+        Cabal-syntax,
         directory <1.4,
         filepath <1.6,
-        optparse-applicative >=0.16 && <0.19,
+        optparse-applicative >=0.16 && <0.20,
         process <1.7
 
-    if flag(cabal-syntax)
-        build-depends: Cabal-syntax
-
-    else
-        build-depends: Cabal
-
 test-suite cabal-add-tests
     type:               exitcode-stdio-1.0
     main-is:            Main.hs
@@ -80,6 +67,24 @@
     ghc-options:        -Wall
     build-depends:
         base <5,
+        Diff >=0.4,
+        directory,
+        process,
+        string-qq,
+        tasty,
+        temporary
+
+test-suite cabal-add-unit-tests
+    type:             exitcode-stdio-1.0
+    main-is:          UnitTests.hs
+    hs-source-dirs:   tests/
+    default-language: GHC2021
+    ghc-options:      -Wall
+    build-depends:
+        base <5,
+        bytestring,
+        Cabal,
+        cabal-add,
         Diff >=0.4,
         directory,
         process,
diff --git a/src/Distribution/Client/Add.hs b/src/Distribution/Client/Add.hs
--- a/src/Distribution/Client/Add.hs
+++ b/src/Distribution/Client/Add.hs
@@ -14,9 +14,10 @@
   resolveComponent,
   CommonStanza (..),
   validateDependency,
-  Config (..),
-  executeConfig,
+  AddConfig (..),
+  executeAddConfig,
   validateChanges,
+  TargetField (..),
 ) where
 
 import Control.Applicative ((<|>))
@@ -28,10 +29,11 @@
 import Data.List qualified as L
 import Data.List.NonEmpty (NonEmpty (..))
 import Data.List.NonEmpty qualified as NE
-import Data.Maybe (fromMaybe, isJust, mapMaybe)
+import Data.Maybe (fromMaybe, isJust, isNothing, mapMaybe)
 import Data.Set (Set)
 import Data.Set qualified as S
 import Distribution.CabalSpecVersion (CabalSpecVersion (CabalSpecV1_0, CabalSpecV3_0))
+import Distribution.Client.Common (CommonStanza (..), TargetField (..), getTargetName, isComponent, splitAtPosition)
 import Distribution.Fields (
   Field (..),
   FieldLine (..),
@@ -45,7 +47,6 @@
   GenericPackageDescription (..),
   LibraryName (..),
   PackageDescription (..),
-  componentNameStanza,
   componentNameString,
   pkgName,
   unPackageName,
@@ -68,29 +69,32 @@
   resolveBuildTargets,
  )
 
--- | Just a newtype wrapper, since @Cabal-syntax@ does not provide any.
-newtype CommonStanza = CommonStanza {unCommonStanza :: ByteString}
-  deriving (Eq, Ord, Show)
-
--- | An input for 'executeConfig'.
-data Config = Config
+-- | An input for 'executeAddConfig'.
+data AddConfig = AddConfig
   { cnfOrigContents :: !ByteString
   -- ^ Original Cabal file (with quirks patched,
   -- see "Distribution.PackageDescription.Quirks"),
   -- must be in sync with 'cnfFields'.
   , cnfFields :: ![Field Position]
-  -- ^ Parsed (by 'readFields' or, more specifically, by 'parseCabalFile')
+  -- ^ Parsed (by 'Distribution.Fields.readFields' or, more specifically, by 'parseCabalFile')
   -- representation of the Cabal file,
   -- must be in sync with 'cnfOrigContents'.
   , cnfComponent :: !(Either CommonStanza ComponentName)
   -- ^ Which component to update?
   -- Usually constructed by 'resolveComponent'.
-  , cnfDependencies :: !(NonEmpty ByteString)
-  -- ^ Which dependencies to add?
+  , cnfTargetField :: !TargetField
+  -- ^ Which field to add the provided content to?
+  , cnfAdditions :: !(NonEmpty ByteString)
+  -- ^ Which content to add to the target field?
   -- Usually constructed by 'validateDependency'.
   }
   deriving (Eq, Show)
 
+requiresCommas :: TargetField -> Bool
+requiresCommas = \case
+  BuildDepends -> True
+  _ -> False
+
 extractComponentNames :: GenericPackageDescription -> Set ComponentName
 extractComponentNames GenericPackageDescription {..} =
   foldMap (const $ S.singleton $ CLibName LMainLibName) condLibrary
@@ -257,7 +261,7 @@
   :: MonadError String m
   => FilePath
   -- ^ File name, just for error reporting.
-  -> ([Field Position], GenericPackageDescription)
+  -> ([Field a], GenericPackageDescription)
   -- ^ Parsed Cabal file, as returned by 'parseCabalFile'.
   -> Maybe String
   -- ^ Component name (or default component if 'Nothing'),
@@ -291,14 +295,19 @@
         "Target component is ambiguous.\n"
           ++ knownTargetsHint
     where
+      allTargets :: Set String
       allTargets =
         S.fromList (mapMaybe (fmap unUnqualComponentName . componentNameString) (S.toList componentNames))
           <> S.map (B.unpack . unCommonStanza) commonStanzas
           <> specialComponents componentNames
+
+      knownTargetsHint :: String
       knownTargetsHint =
         "Specify one with -c: "
           ++ L.intercalate ", " (S.toList allTargets)
           ++ "."
+
+      resolution :: Resolution (Either CommonStanza ComponentName)
       resolution =
         fmap Right (resolveToComponentName componentNames component)
           <> fmap Left (resolveToCommonStanza commonStanzas component)
@@ -328,38 +337,9 @@
         ++ "' because:\n"
         ++ err
 
--- Both lines and rows are 1-based.
-splitAtPosition :: Position -> ByteString -> (ByteString, ByteString)
-splitAtPosition (Position line row) bs
-  | line <= 1 = B.splitAt (row - 1) bs
-  | otherwise = case L.drop (line - 2) nls of
-      [] -> (bs, mempty)
-      nl : _ -> B.splitAt (nl + row) bs
-  where
-    nls = B.elemIndices '\n' bs
-
 splitAtPositionLine :: Position -> ByteString -> (ByteString, ByteString)
 splitAtPositionLine (Position line _row) = splitAtPosition (Position line 1)
 
-isComponent :: Either CommonStanza ComponentName -> Field a -> Bool
-isComponent (Right cmp) = \case
-  Section (Name _ "library") [] _subFields
-    | cmp == CLibName LMainLibName ->
-        True
-  Section (Name _ sectionName) [SecArgName _pos sectionArg] _subFields
-    | sectionName <> " " <> sectionArg == B.pack (componentNameStanza cmp) ->
-        True
-  Section (Name _ sectionName) [SecArgStr _pos sectionArg] _subFields
-    | sectionName <> " " <> sectionArg == B.pack (componentNameStanza cmp) ->
-        True
-  _ -> False
-isComponent (Left (CommonStanza commonName)) = \case
-  Section (Name _ "common") [SecArgName _pos sectionArg] _subFields ->
-    sectionArg == commonName
-  Section (Name _ "common") [SecArgStr _pos sectionArg] _subFields ->
-    sectionArg == commonName
-  _ -> False
-
 findNonImportField :: [Field Position] -> Maybe Position
 findNonImportField (Section _ _ subFields : rest) =
   case filter (not . isImportField) subFields of
@@ -385,31 +365,34 @@
   Field (Name ann _) _ -> ann
   Section (Name ann _) _ _ -> ann
 
-isBuildDependsField :: Field ann -> Bool
-isBuildDependsField = \case
-  Field (Name _ "build-depends") _ -> True
+isTargetField :: ByteString -> Field ann -> Bool
+isTargetField name = \case
+  Field (Name _ fieldName) _ -> name == fieldName
   _ -> False
 
-detectLeadingComma :: ByteString -> Maybe ByteString
-detectLeadingComma xs = case B.uncons xs of
+detectLeadingSeparator :: ByteString -> Maybe ByteString
+detectLeadingSeparator xs = case B.uncons xs of
   Just (',', ys) -> Just $ B.cons ',' $ B.takeWhile (== ' ') ys
+  Just (' ', ys) -> Just $ B.takeWhile (== ' ') ys
   _ -> Nothing
 
+isCommaSeparated :: ByteString -> Bool
+isCommaSeparated xs = ',' `B.elem` xs
+
 dropRepeatingSpaces :: ByteString -> ByteString
 dropRepeatingSpaces xs = case B.uncons xs of
   Just (' ', ys) -> B.cons ' ' (B.dropWhile (== ' ') ys)
   _ -> xs
 
--- | Find build-depends section and insert new
--- dependencies at the beginning, trying our best
+-- | Find a target section and insert new
+-- fields at the beginning, trying our best
 -- to preserve formatting. This often breaks however
--- if there are comments in between build-depends.
-fancyAlgorithm :: Config -> Maybe ByteString
-fancyAlgorithm Config {cnfFields, cnfComponent, cnfOrigContents, cnfDependencies} = do
-  component <- L.find (isComponent cnfComponent) cnfFields
-  Section _ _ subFields <- pure component
-  buildDependsField <- L.find isBuildDependsField subFields
-  Field _ (FieldLine firstDepPos _dep : restDeps) <- pure buildDependsField
+-- if there are comments in between target fields.
+fancyAddAlgorithm :: AddConfig -> Maybe ByteString
+fancyAddAlgorithm AddConfig {cnfFields, cnfComponent, cnfOrigContents, cnfAdditions, cnfTargetField} = do
+  subFields : _ <- pure $ mapMaybe (isComponent cnfComponent) cnfFields
+  targetField <- L.find (isTargetField $ getTargetName cnfTargetField) subFields
+  Field _ (FieldLine firstDepPos _dep : restDeps) <- pure targetField
 
   -- This is not really the second dependency:
   -- it's a dependency on the next line.
@@ -418,14 +401,15 @@
         _ -> Nothing
       fillerPred c = isSpaceChar8 c || c == ','
 
-  let (B.takeWhileEnd fillerPred -> pref, B.takeWhile fillerPred -> suff) =
-        splitAtPosition firstDepPos cnfOrigContents
+  let (rawPref, rawSuff) = splitAtPosition firstDepPos cnfOrigContents
+      pref = B.takeWhileEnd fillerPred rawPref
+      suff = B.takeWhile fillerPred rawSuff
       prefSuff = pref <> suff
-
+      commaSeparation = isCommaSeparated rawSuff || requiresCommas cnfTargetField
       (afterLast, inBetween, beforeFirst) = case secondDepPos of
         Nothing ->
-          ( if B.any (== ',') prefSuff then pref' else "," <> pref'
-          , if B.any (== ',') prefSuff then prefSuff' else "," <> prefSuff'
+          ( if B.any (== ',') prefSuff || not commaSeparation then pref' else "," <> pref'
+          , if B.any (== ',') prefSuff || not commaSeparation then prefSuff' else "," <> prefSuff'
           , suff
           )
           where
@@ -442,39 +426,39 @@
               splitAtPosition pos cnfOrigContents
 
   let (beforeFirstDep, afterFirstDep) = splitAtPosition firstDepPos cnfOrigContents
-      newBuildDeps = beforeFirst <> B.intercalate inBetween (NE.toList cnfDependencies) <> afterLast
+      newFieldContents = beforeFirst <> B.intercalate inBetween (NE.toList cnfAdditions) <> afterLast
 
-  let ret = beforeFirstDep <> newBuildDeps <> afterFirstDep
+  let ret = beforeFirstDep <> newFieldContents <> afterFirstDep
   pure ret
 
--- | Find build-depends section and insert new
--- dependencies at the beginning. Very limited effort
+-- | Find a target section and insert new
+-- fields at the beginning. Very limited effort
 -- is put into preserving formatting.
-niceAlgorithm :: Config -> Maybe ByteString
-niceAlgorithm Config {cnfFields, cnfComponent, cnfOrigContents, cnfDependencies} = do
-  component <- L.find (isComponent cnfComponent) cnfFields
-  Section _ _ subFields <- pure component
-  buildDependsField <- L.find isBuildDependsField subFields
-  Field _ (FieldLine pos _dep : _) <- pure buildDependsField
+niceAddAlgorithm :: AddConfig -> Maybe ByteString
+niceAddAlgorithm AddConfig {cnfFields, cnfComponent, cnfOrigContents, cnfAdditions, cnfTargetField} = do
+  subFields : _ <- pure $ mapMaybe (isComponent cnfComponent) cnfFields
+  targetField <- L.find (isTargetField (getTargetName cnfTargetField)) subFields
+  Field _ (FieldLine pos _dep : _) <- pure targetField
 
   let (before, after) = splitAtPosition pos cnfOrigContents
-      (_, buildDepsHeader) = splitAtPosition (getFieldNameAnn buildDependsField) before
-      filler = dropRepeatingSpaces $ B.drop 1 $ B.dropWhile (/= ':') buildDepsHeader
-      leadingCommaStyle = detectLeadingComma after
-      filler' = maybe ("," <> filler) (filler <>) leadingCommaStyle
-      newBuildDeps =
-        fromMaybe "" leadingCommaStyle
-          <> B.intercalate filler' (NE.toList cnfDependencies)
-          <> (if isJust leadingCommaStyle then filler else filler')
+      (_, targetHeader) = splitAtPosition (getFieldNameAnn targetField) before
+      leadingSeparatorStyle = detectLeadingSeparator after
+      filler = dropRepeatingSpaces $ B.drop 1 $ B.dropWhile (/= ':') targetHeader
+      defaultSep = if isCommaSeparated after || cnfTargetField == BuildDepends then "," else ""
+      filler' = maybe (defaultSep <> filler) (filler <>) leadingSeparatorStyle
+      newFieldContents =
+        fromMaybe "" leadingSeparatorStyle
+          <> B.intercalate filler' (NE.toList cnfAdditions)
+          <> (if isJust leadingSeparatorStyle then filler else filler')
   pure $
-    before <> newBuildDeps <> after
+    before <> newFieldContents <> after
 
--- | Introduce a new build-depends section
+-- | Introduce a new target section
 -- after the last common stanza import.
 -- This is not fancy, but very robust.
-roughAlgorithm :: Config -> Maybe ByteString
-roughAlgorithm Config {cnfFields, cnfComponent, cnfOrigContents, cnfDependencies} = do
-  let componentAndRest = L.dropWhile (not . isComponent cnfComponent) cnfFields
+roughAddAlgorithm :: AddConfig -> Maybe ByteString
+roughAddAlgorithm AddConfig {cnfFields, cnfComponent, cnfOrigContents, cnfAdditions, cnfTargetField} = do
+  let componentAndRest = L.dropWhile (isNothing . isComponent cnfComponent) cnfFields
   pos@(Position _ row) <- findNonImportField componentAndRest
   let (before, after) = splitAtPositionLine pos cnfOrigContents
       lineEnding' = B.takeWhileEnd isSpaceChar8 before
@@ -483,24 +467,24 @@
       buildDeps =
         (if needsNewlineBefore then lineEnding else "")
           <> B.replicate (row - 1) ' '
-          <> "build-depends: "
-          <> B.intercalate ", " (NE.toList cnfDependencies)
+          <> (getTargetName cnfTargetField <> ": ")
+          <> B.intercalate ", " (NE.toList cnfAdditions)
           <> lineEnding
   pure $
     before <> buildDeps <> after
 
--- | The main workhorse, adding dependencies to a specified component
+-- | The main workhorse, adding fields to a specified component
 -- in the Cabal file.
-executeConfig
+executeAddConfig
   :: (Either CommonStanza ComponentName -> ByteString -> Bool)
   -- ^ How to validate results? See 'validateChanges'.
-  -> Config
+  -> AddConfig
   -- ^ Input arguments.
   -> Maybe ByteString
   -- ^ Updated contents, if validated successfully.
-executeConfig validator cnf@Config {cnfComponent} =
+executeAddConfig validator cnf@AddConfig {cnfComponent} =
   L.find (validator cnfComponent) $
-    mapMaybe ($ cnf) [fancyAlgorithm, niceAlgorithm, roughAlgorithm]
+    mapMaybe ($ cnf) [fancyAddAlgorithm, niceAddAlgorithm, roughAddAlgorithm]
 
 -- | Validate that updates did not cause unexpected effects on other sections
 -- of the Cabal file.
@@ -511,7 +495,7 @@
   -- ^ Which component was supposed to be updated?
   -- Usually constructed by 'resolveComponent'.
   -> ByteString
-  -- ^ Update Cabal file.
+  -- ^ Updated Cabal file.
   -> Bool
   -- ^ Was the update successful?
 validateChanges origPackDesc (Left _commonStanza) newContents =
diff --git a/src/Distribution/Client/Common.hs b/src/Distribution/Client/Common.hs
new file mode 100644
--- /dev/null
+++ b/src/Distribution/Client/Common.hs
@@ -0,0 +1,80 @@
+{-# LANGUAGE ImportQualifiedPost #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+
+-- |
+-- Copyright:   (c) 2023 Bodigrim
+-- License:     BSD-3-Clause
+module Distribution.Client.Common (
+  CommonStanza (..),
+  isComponent,
+  splitAtPosition,
+  TargetField (..),
+  getTargetName,
+) where
+
+import Data.ByteString (ByteString)
+import Data.ByteString.Char8 qualified as B
+import Data.List qualified as L
+import Distribution.Fields (
+  Field (..),
+  Name (..),
+  SectionArg (..),
+ )
+import Distribution.PackageDescription (
+  ComponentName (..),
+  LibraryName (..),
+  componentNameStanza,
+ )
+import Distribution.Parsec.Position (Position (..))
+
+-- | Just a newtype wrapper, since @Cabal-syntax@ does not provide any.
+newtype CommonStanza = CommonStanza {unCommonStanza :: ByteString}
+  deriving (Eq, Ord, Show)
+
+isComponent :: Either CommonStanza ComponentName -> Field a -> Maybe [Field a]
+isComponent (Right cmp) = \case
+  Section (Name _ "library") [] subFields
+    | cmp == CLibName LMainLibName ->
+        Just subFields
+  Section (Name _ sectionName) [SecArgName _pos sectionArg] subFields
+    | sectionName <> " " <> sectionArg == B.pack (componentNameStanza cmp) ->
+        Just subFields
+  Section (Name _ sectionName) [SecArgStr _pos sectionArg] subFields
+    | sectionName <> " " <> sectionArg == B.pack (componentNameStanza cmp) ->
+        Just subFields
+  _ -> Nothing
+isComponent (Left (CommonStanza commonName)) = \case
+  Section (Name _ "common") [SecArgName _pos sectionArg] subFields
+    | sectionArg == commonName ->
+        Just subFields
+  Section (Name _ "common") [SecArgStr _pos sectionArg] subFields
+    | sectionArg == commonName ->
+        Just subFields
+  _ -> Nothing
+
+-- Both lines and rows are 1-based.
+splitAtPosition :: Position -> ByteString -> (ByteString, ByteString)
+splitAtPosition (Position line row) bs
+  | line <= 1 = B.splitAt (row - 1) bs
+  | otherwise = case L.drop (line - 2) nls of
+      [] -> (bs, mempty)
+      nl : _ -> B.splitAt (nl + row) bs
+  where
+    nls = B.elemIndices '\n' bs
+
+-- | A field in a cabal file, new content can be added to
+data TargetField
+  = -- | Corresponds to @build-depends@ in the cabal file
+    BuildDepends
+  | -- | Corresponds to @exposed-modules@ in the cabal file
+    ExposedModules
+  | -- | Corresponds to @other-modules@ in the cabal file
+    OtherModules
+  deriving (Eq, Show, Ord)
+
+getTargetName :: TargetField -> ByteString
+getTargetName = \case
+  BuildDepends -> "build-depends"
+  ExposedModules -> "exposed-modules"
+  OtherModules -> "other-modules"
diff --git a/src/Distribution/Client/Rename.hs b/src/Distribution/Client/Rename.hs
new file mode 100644
--- /dev/null
+++ b/src/Distribution/Client/Rename.hs
@@ -0,0 +1,144 @@
+{-# LANGUAGE ImportQualifiedPost #-}
+{-# LANGUAGE LambdaCase #-}
+
+-- |
+-- Copyright:   (c) 2023 Bodigrim
+-- License:     BSD-3-Clause
+module Distribution.Client.Rename (
+  parseCabalFile,
+  resolveComponent,
+  CommonStanza (..),
+  validateDependency,
+  RenameConfig (..),
+  executeRenameConfig,
+  validateChanges,
+  TargetField (..),
+) where
+
+import Data.ByteString (ByteString)
+import Data.ByteString.Char8 qualified as B
+import Data.Char (isPunctuation, isSpace)
+import Data.Foldable (fold)
+import Data.List qualified as L
+import Distribution.Client.Add (
+  TargetField (..),
+  parseCabalFile,
+  resolveComponent,
+  validateChanges,
+  validateDependency,
+ )
+import Distribution.Client.Common (CommonStanza (..), getTargetName, isComponent, splitAtPosition)
+import Distribution.Fields (
+  Field (..),
+  FieldLine (..),
+  Name (..),
+  SectionArg (..),
+ )
+import Distribution.PackageDescription (
+  ComponentName (..),
+ )
+import Distribution.Parsec (
+  Position (..),
+ )
+
+-- | An input for 'executeRenameConfig'.
+data RenameConfig = RenameConfig
+  { cnfOrigContents :: !ByteString
+  -- ^ Original Cabal file (with quirks patched,
+  -- see "Distribution.PackageDescription.Quirks"),
+  -- must be in sync with 'cnfFields'.
+  , cnfFields :: ![Field Position]
+  -- ^ Parsed (by 'Distribution.Fields.readFields' or, more specifically, by 'parseCabalFile')
+  -- representation of the Cabal file,
+  -- must be in sync with 'cnfOrigContents'.
+  , cnfComponent :: !(Either CommonStanza ComponentName)
+  -- ^ Which component to update?
+  -- Usually constructed by 'resolveComponent'.
+  , cnfTargetField :: !TargetField
+  -- ^ In which field to rename the provided content?
+  , cnfRenameFrom :: !ByteString
+  -- ^ Rename what?
+  , cnfRenameTo :: !ByteString
+  -- ^ Rename to what?
+  }
+  deriving (Eq, Show)
+
+-- | The main workhorse, renaming fields in a specified component
+-- in the Cabal file.
+executeRenameConfig
+  :: (Either CommonStanza ComponentName -> ByteString -> Bool)
+  -- ^ How to validate results? See 'validateChanges'.
+  -> RenameConfig
+  -- ^ Input arguments.
+  -> Maybe ByteString
+  -- ^ Updated contents, if validated successfully.
+executeRenameConfig !_ RenameConfig {cnfRenameFrom}
+  | B.null cnfRenameFrom = Nothing
+executeRenameConfig validator RenameConfig {cnfFields, cnfComponent, cnfOrigContents, cnfRenameFrom, cnfRenameTo, cnfTargetField} = do
+  let fieldsWithSource = annotateFieldsWithSource cnfOrigContents cnfFields
+      fieldsWithSource' = map replaceInSection fieldsWithSource
+      newContents = foldMap fold fieldsWithSource'
+  if validator cnfComponent newContents then Just newContents else Nothing
+  where
+    replaceInBS :: ByteString -> ByteString
+    replaceInBS hay
+      | B.null rest =
+          hay
+      | not startsWithBoundary || not endsWithBoundary =
+          pref <> cnfRenameFrom <> replaceInBS suff
+      | otherwise =
+          pref <> cnfRenameTo <> replaceInBS suff
+      where
+        (pref, rest) = B.breakSubstring cnfRenameFrom hay
+        suff = B.drop (B.length cnfRenameFrom) rest
+        isTokenBoundary c = (isSpace c || isPunctuation c || c `elem` "^>=<") && c /= '-' && c /= '.'
+        startsWithBoundary = maybe True (isTokenBoundary . snd) (B.unsnoc pref)
+        endsWithBoundary = maybe True (isTokenBoundary . fst) (B.uncons suff)
+
+    replaceInFieldLine :: FieldLine ByteString -> FieldLine ByteString
+    replaceInFieldLine (FieldLine ann cnt) = FieldLine (replaceInBS ann) (replaceInBS cnt)
+
+    replaceInField :: Field ByteString -> Field ByteString
+    replaceInField = \case
+      Field name@(Name _ann fieldName) fls
+        | fieldName == getTargetName cnfTargetField ->
+            Field name (map replaceInFieldLine fls)
+      fld@Field {} -> fld
+      Section name args subFields -> Section name args (map replaceInField subFields)
+
+    replaceInSection :: Field ByteString -> Field ByteString
+    replaceInSection = \case
+      sct@(Section name args subFields) -> Section name args (map func subFields)
+        where
+          func = case isComponent cnfComponent sct of
+            Nothing -> replaceInSection
+            Just {} -> replaceInField
+      fld@Field {} -> fld
+
+annotateFieldsWithSource :: ByteString -> [Field Position] -> [Field ByteString]
+annotateFieldsWithSource bs = snd . L.mapAccumR annotateField maxBoundPos
+  where
+    annotateField :: Position -> Field Position -> (Position, Field ByteString)
+    annotateField finishPos = \case
+      Field (Name pos name) fls -> (pos, Field (Name (getSrcBetween pos finishPos') name) fls')
+        where
+          (finishPos', fls') = L.mapAccumR annotateFieldLine finishPos fls
+      Section (Name pos name) args fs -> (pos, Section (Name (getSrcBetween pos finishPos'') name) args' fs')
+        where
+          (finishPos', fs') = L.mapAccumR annotateField finishPos fs
+          (finishPos'', args') = L.mapAccumR annotateSectionArg finishPos' args
+
+    annotateFieldLine :: Position -> FieldLine Position -> (Position, FieldLine ByteString)
+    annotateFieldLine finishPos (FieldLine pos xs) = (pos, FieldLine (getSrcBetween pos finishPos) xs)
+
+    annotateSectionArg :: Position -> SectionArg Position -> (Position, SectionArg ByteString)
+    annotateSectionArg finishPos = \case
+      SecArgName pos xs -> (pos, SecArgName (getSrcBetween pos finishPos) xs)
+      SecArgStr pos xs -> (pos, SecArgStr (getSrcBetween pos finishPos) xs)
+      SecArgOther pos xs -> (pos, SecArgOther (getSrcBetween pos finishPos) xs)
+
+    getSrcBetween :: Position -> Position -> ByteString
+    getSrcBetween from to = snd $ splitAtPosition from $ fst $ splitAtPosition to bs
+
+    maxBoundPos :: Position
+    maxBoundPos = Position maxBound maxBound
diff --git a/tests/Main.hs b/tests/Main.hs
--- a/tests/Main.hs
+++ b/tests/Main.hs
@@ -14,13 +14,14 @@
 import System.Directory (findExecutable)
 import System.Exit (ExitCode (..))
 import System.IO.Temp (withSystemTempDirectory)
-import System.Process (cwd, proc, readCreateProcessWithExitCode)
+import System.Process (cwd, env, proc, readCreateProcessWithExitCode)
 import Test.Tasty (TestTree, defaultMain, testGroup)
 import Test.Tasty.Providers (IsTest (..), singleTest, testFailed, testPassed)
 
 data CabalAddTest = CabalAddTest
   { catName :: String
   , catArgs :: [String]
+  , catEnv :: [(String, String)]
   , catInput :: String
   , catOutput :: String
   }
@@ -36,7 +37,7 @@
         withSystemTempDirectory template $ \tempDir -> do
           let cabalFileName = tempDir ++ "/" ++ template ++ ".cabal"
           writeFile cabalFileName catInput
-          let crpr = (proc cabalAddExe catArgs) {cwd = Just tempDir}
+          let crpr = (proc cabalAddExe catArgs) {cwd = Just tempDir, env = Just catEnv}
           (code, _out, err) <- readCreateProcessWithExitCode crpr ""
           case code of
             ExitFailure {} -> pure $ testFailed err
@@ -66,6 +67,7 @@
     CabalAddTest
       { catName = "add multiple dependencies 1"
       , catArgs = ["foo < 1 && >0.7", "baz ^>= 2.0"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -98,6 +100,7 @@
     CabalAddTest
       { catName = "add multiple dependencies 2"
       , catArgs = ["foo < 1 && >0.7", "baz ^>= 2.0"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -126,6 +129,7 @@
     CabalAddTest
       { catName = "add multiple dependencies 3"
       , catArgs = ["foo < 1 && >0.7", "baz ^>= 2.0"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -158,6 +162,7 @@
     CabalAddTest
       { catName = "add multiple dependencies 4"
       , catArgs = ["foo < 1 && >0.7", "baz ^>= 2.0"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -192,6 +197,7 @@
     CabalAddTest
       { catName = "word 'library' in description"
       , catArgs = ["foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -228,6 +234,7 @@
     CabalAddTest
       { catName = "import fields 1"
       , catArgs = ["foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 2.2
@@ -265,6 +272,7 @@
     CabalAddTest
       { catName = "import fields 2"
       , catArgs = ["foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 2.2
@@ -302,6 +310,7 @@
     CabalAddTest
       { catName = "import fields 3"
       , catArgs = ["foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 2.2
@@ -337,6 +346,7 @@
     CabalAddTest
       { catName = "sublibrary target 1"
       , catArgs = ["foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -369,6 +379,7 @@
     CabalAddTest
       { catName = "sublibrary target 2"
       , catArgs = ["baz", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -409,6 +420,7 @@
     CabalAddTest
       { catName = "executable target 1"
       , catArgs = ["exe", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -443,6 +455,7 @@
     CabalAddTest
       { catName = "executable target 2"
       , catArgs = ["baz", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -477,6 +490,7 @@
     CabalAddTest
       { catName = "executable target 3"
       , catArgs = ["baz", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -511,6 +525,7 @@
     CabalAddTest
       { catName = "executable target 4"
       , catArgs = ["baz", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -551,6 +566,7 @@
     CabalAddTest
       { catName = "test target 1"
       , catArgs = ["baz", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -593,6 +609,7 @@
     CabalAddTest
       { catName = "test target 2"
       , catArgs = ["test:baz", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -635,6 +652,7 @@
     CabalAddTest
       { catName = "common stanza as a target 1"
       , catArgs = ["foo", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -664,6 +682,7 @@
     CabalAddTest
       { catName = "common stanza as a target 2"
       , catArgs = ["foo", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -700,6 +719,7 @@
     CabalAddTest
       { catName = "two spaces in stanza"
       , catArgs = ["baz", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -734,6 +754,7 @@
     CabalAddTest
       { catName = "title case in stanza 1"
       , catArgs = ["foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -766,6 +787,7 @@
     CabalAddTest
       { catName = "title case in stanza 2"
       , catArgs = ["baz", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -800,6 +822,7 @@
     CabalAddTest
       { catName = "title case in build-depends"
       , catArgs = ["baz", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -834,6 +857,7 @@
     CabalAddTest
       { catName = "shared component prefixes"
       , catArgs = ["baz", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 name:          dummy
@@ -878,6 +902,7 @@
     CabalAddTest
       { catName = "Windows line endings"
       , catArgs = ["exe", "foo < 1 && >0.7", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           convertToWindowsLineEndings
             [s|
@@ -912,6 +937,7 @@
     CabalAddTest
       { catName = "build-depends start from comma 1"
       , catArgs = ["baz ^>= 2.0", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -944,6 +970,7 @@
     CabalAddTest
       { catName = "build-depends start from comma 2"
       , catArgs = ["baz ^>= 2.0", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -972,6 +999,7 @@
     CabalAddTest
       { catName = "build-depends start from comma 3"
       , catArgs = ["baz ^>= 2.0", "quux > 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1004,6 +1032,7 @@
     CabalAddTest
       { catName = "build-depends are under condition"
       , catArgs = ["baz ^>= 2.0", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1037,6 +1066,7 @@
     CabalAddTest
       { catName = "empty component 1"
       , catArgs = ["baz ^>= 2.0", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1071,6 +1101,7 @@
     CabalAddTest
       { catName = "empty component 2"
       , catArgs = ["baz ^>= 2.0", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1098,6 +1129,7 @@
     CabalAddTest
       { catName = "empty component 3"
       , catArgs = ["baz ^>= 2.0", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1124,6 +1156,7 @@
     CabalAddTest
       { catName = "empty build-depends"
       , catArgs = ["baz ^>= 2.0", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1153,6 +1186,7 @@
     CabalAddTest
       { catName = "component in figure braces"
       , catArgs = ["baz ^>= 2.0", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1183,6 +1217,7 @@
     CabalAddTest
       { catName = "comments with commas"
       , catArgs = ["baz ^>= 2.0", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1219,6 +1254,7 @@
     CabalAddTest
       { catName = "comments without commas"
       , catArgs = ["baz ^>= 2.0", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1253,6 +1289,7 @@
     CabalAddTest
       { catName = "all build-deps on the same line"
       , catArgs = ["baz ^>= 2.0", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1281,6 +1318,7 @@
     CabalAddTest
       { catName = "ignore add as the first command-line argument"
       , catArgs = ["add", "baz ^>= 2.0", "quux < 1"]
+      , catEnv = [("CABAL", "/fake/usr/bin/local/cabal")]
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1309,6 +1347,7 @@
     CabalAddTest
       { catName = "do not ignore add as the second command-line argument"
       , catArgs = ["baz ^>= 2.0", "add", "quux < 1"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1337,6 +1376,7 @@
     CabalAddTest
       { catName = "sublibrary as a dependency"
       , catArgs = ["foo:bar"]
+      , catEnv = mempty
       , catInput =
           [s|
 cabal-version: 3.6
@@ -1359,6 +1399,38 @@
 |]
       }
 
+caseSpecialDependencyName1 :: TestTree
+caseSpecialDependencyName1 =
+  mkTest $
+    CabalAddTest
+      { catName = "add dependency named 'add'"
+      , catArgs = ["add"]
+      , catEnv = mempty
+      , catInput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    base >=4.15 && <5
+|]
+      , catOutput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    add,
+    base >=4.15 && <5
+|]
+      }
+
 main :: IO ()
 main =
   defaultMain $
@@ -1403,4 +1475,5 @@
       , caseIgnoreAddArgument
       , caseDoNotIgnoreAddArgument
       , caseSublibraryDependency
+      , caseSpecialDependencyName1
       ]
diff --git a/tests/UnitTests.hs b/tests/UnitTests.hs
new file mode 100644
--- /dev/null
+++ b/tests/UnitTests.hs
@@ -0,0 +1,676 @@
+{-# LANGUAGE ImportQualifiedPost #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE QuasiQuotes #-}
+{-# LANGUAGE RecordWildCards #-}
+
+-- |
+-- Copyright:   (c) 2023 Bodigrim
+-- License:     BSD-3-Clause
+module Main (main) where
+
+import Data.Algorithm.Diff (Diff, PolyDiff (..), getDiff)
+import Data.ByteString.Char8 qualified as B
+import Data.List.NonEmpty qualified as NE
+import Data.Maybe (mapMaybe)
+import Data.String.QQ (s)
+import Distribution.Client.Add (AddConfig (..), TargetField (..), executeAddConfig, parseCabalFile)
+import Distribution.Client.Rename (RenameConfig (..), executeRenameConfig)
+import Distribution.Fields.Field (Field)
+import Distribution.PackageDescription (ComponentName (..), LibraryName (..))
+import Distribution.Parsec.Position (Position)
+import Test.Tasty (TestTree, defaultMain, testGroup)
+import Test.Tasty.Providers (IsTest (..), singleTest, testFailed, testPassed)
+
+data CabalAddTest = CabalAddTest
+  { catName :: String
+  , catConfig :: AddConfig
+  , catOutput :: String
+  }
+
+instance IsTest CabalAddTest where
+  testOptions = pure []
+
+  run _opts CabalAddTest {..} _yieldProgress = do
+    let outputM = executeAddConfig (const $ const True) catConfig
+    case outputM of
+      Nothing -> pure $ testFailed "config could not be applied"
+      Just output ->
+        pure $
+          if B.unpack output == catOutput
+            then testPassed ""
+            else testFailed $ prettyDiff $ getDiff (lines catOutput) (lines (B.unpack output))
+
+data CabalRenameTest = CabalRenameTest
+  { crtName :: String
+  , crtConfig :: RenameConfig
+  , crtOutput :: String
+  }
+
+instance IsTest CabalRenameTest where
+  testOptions = pure []
+
+  run _opts CabalRenameTest {..} _yieldProgress = do
+    let outputM = executeRenameConfig (const $ const True) crtConfig
+    case outputM of
+      Nothing -> pure $ testFailed "config could not be applied"
+      Just output ->
+        pure $
+          if B.unpack output == crtOutput
+            then testPassed ""
+            else testFailed $ prettyDiff $ getDiff (lines crtOutput) (lines (B.unpack output))
+
+parseCabalFileOrError :: B.ByteString -> [Field Position]
+parseCabalFileOrError inContents = case parseCabalFile "" inContents of
+  Right (fields, _) -> fields
+  Left err -> error $ "Failed to parse cabal file with error: " <> err
+
+caseMultipleBuildDependencies1 :: TestTree
+caseMultipleBuildDependencies1 =
+  mkAddTest $
+    CabalAddTest
+      { catName = "add multiple dependencies 1"
+      , catConfig =
+          AddConfig
+            { cnfComponent = Right $ CLibName LMainLibName
+            , cnfAdditions = NE.fromList ["foo < 1 && >0.7", "baz ^>= 2.0"]
+            , cnfTargetField = BuildDepends
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            }
+      , catOutput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    foo < 1 && >0.7,
+    baz ^>= 2.0,
+    base >=4.15 && <5
+|]
+      }
+  where
+    inContents =
+      [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    base >=4.15 && <5
+|]
+
+caseMultipleExposedModules1 :: TestTree
+caseMultipleExposedModules1 =
+  mkAddTest $
+    CabalAddTest
+      { catName = "add multiple exposed modules 1"
+      , catConfig =
+          AddConfig
+            { cnfComponent = Right $ CLibName LMainLibName
+            , cnfAdditions = NE.fromList ["Test.Mod1", "Test.Mod2"]
+            , cnfTargetField = ExposedModules
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            }
+      , catOutput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Test.Mod1, Test.Mod2, Main, OtherModule.Mine
+|]
+      }
+  where
+    inContents =
+      [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Main, OtherModule.Mine
+|]
+
+caseMultipleExposedModulesUsingSpaces :: TestTree
+caseMultipleExposedModulesUsingSpaces =
+  mkAddTest $
+    CabalAddTest
+      { catName = "add multiple exposed modules with spaces"
+      , catConfig =
+          AddConfig
+            { cnfComponent = Right $ CLibName LMainLibName
+            , cnfAdditions = NE.fromList ["Test.Mod1", "Test.Mod2"]
+            , cnfTargetField = ExposedModules
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            }
+      , catOutput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Test.Mod1 Test.Mod2 Main OtherModule.Mine
+|]
+      }
+  where
+    inContents =
+      [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Main OtherModule.Mine
+|]
+
+caseMultipleOtherModules :: TestTree
+caseMultipleOtherModules =
+  mkAddTest $
+    CabalAddTest
+      { catName = "add multiple other modules"
+      , catConfig =
+          AddConfig
+            { cnfComponent = Right $ CTestName "testss"
+            , cnfAdditions = NE.fromList ["Test.Mod1", "Mod3"]
+            , cnfTargetField = OtherModules
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            }
+      , catOutput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Test.Mod1 Test.Mod2
+test-suite testss
+  main-is: Main.hs
+  type: exitcode-stdio-1.0
+  other-modules:
+    Test.Mod1,
+    Mod3,
+    Dir.Mod1,
+    Dir.Mod2
+|]
+      }
+  where
+    inContents =
+      [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Test.Mod1 Test.Mod2
+test-suite testss
+  main-is: Main.hs
+  type: exitcode-stdio-1.0
+  other-modules:
+    Dir.Mod1,
+    Dir.Mod2
+|]
+
+caseMultipleOtherModulesUsingSpaces :: TestTree
+caseMultipleOtherModulesUsingSpaces =
+  mkAddTest $
+    CabalAddTest
+      { catName = "add multiple other modules with space separators"
+      , catConfig =
+          AddConfig
+            { cnfComponent = Right $ CTestName "testss"
+            , cnfAdditions = NE.fromList ["Test.Mod1", "Mod3"]
+            , cnfTargetField = OtherModules
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            }
+      , catOutput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+test-suite testss
+  main-is: Main.hs
+  type: exitcode-stdio-1.0
+  other-modules:
+    Test.Mod1
+    Mod3
+    Dir.Mod1
+    Dir.Mod2
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Test.Mod1, Test.Mod2
+|]
+      }
+  where
+    inContents =
+      [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+test-suite testss
+  main-is: Main.hs
+  type: exitcode-stdio-1.0
+  other-modules:
+    Dir.Mod1
+    Dir.Mod2
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Test.Mod1, Test.Mod2
+|]
+
+caseMultipleOtherModulesUsingLeadingCommas :: TestTree
+caseMultipleOtherModulesUsingLeadingCommas =
+  mkAddTest $
+    CabalAddTest
+      { catName = "add multiple other modules preserving leading commas"
+      , catConfig =
+          AddConfig
+            { cnfComponent = Right $ CTestName "testss"
+            , cnfAdditions = NE.fromList ["Test.Mod1", "Mod3"]
+            , cnfTargetField = OtherModules
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            }
+      , catOutput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+test-suite testss
+  main-is: Main.hs
+  type: exitcode-stdio-1.0
+  other-modules:  Test.Mod1
+                , Mod3
+                , Dir.Mod1
+                , Dir.Mod2
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Test.Mod1, Test.Mod2
+|]
+      }
+  where
+    inContents =
+      [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+test-suite testss
+  main-is: Main.hs
+  type: exitcode-stdio-1.0
+  other-modules:  Dir.Mod1
+                , Dir.Mod2
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Test.Mod1, Test.Mod2
+|]
+
+caseMultipleOtherModulesUsingLeadingSpaces :: TestTree
+caseMultipleOtherModulesUsingLeadingSpaces =
+  mkAddTest $
+    CabalAddTest
+      { catName = "add multiple other modules preserving leading spaces"
+      , catConfig =
+          AddConfig
+            { cnfComponent = Right $ CTestName "testss"
+            , cnfAdditions = NE.fromList ["Test.Mod1", "Mod3"]
+            , cnfTargetField = OtherModules
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            }
+      , catOutput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+test-suite testss
+  main-is: Main.hs
+  type: exitcode-stdio-1.0
+  other-modules:  Test.Mod1
+                  Mod3
+                  Dir.Mod1
+                  Dir.Mod2
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Test.Mod1, Test.Mod2
+|]
+      }
+  where
+    inContents =
+      [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+test-suite testss
+  main-is: Main.hs
+  type: exitcode-stdio-1.0
+  other-modules:  Dir.Mod1
+                  Dir.Mod2
+
+library
+  build-depends:
+    base >=4.15 && <5
+  exposed-modules: Test.Mod1, Test.Mod2
+|]
+
+caseMultipleOtherModulesWithImportFields :: TestTree
+caseMultipleOtherModulesWithImportFields =
+  mkAddTest $
+    CabalAddTest
+      { catName = "add multiple other modules with import field"
+      , catConfig =
+          AddConfig
+            { cnfComponent = Right $ CLibName LMainLibName
+            , cnfAdditions = NE.fromList ["This.Dir.Mod1", "Mod3"]
+            , cnfTargetField = OtherModules
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            }
+      , catOutput =
+          [s|
+cabal-version: 2.2
+name:          dummy
+version:       0.13.0.0
+build-type:    Simple
+
+common foo
+  build-depends: bar
+  other-modules: Other
+
+library
+  import: foo
+  other-modules: This.Dir.Mod1, Mod3
+  build-depends: foo < 1 && >0.7, quux < 1
+  exposed-modules: Foo
+|]
+      }
+  where
+    inContents =
+      [s|
+cabal-version: 2.2
+name:          dummy
+version:       0.13.0.0
+build-type:    Simple
+
+common foo
+  build-depends: bar
+  other-modules: Other
+
+library
+  import: foo
+  build-depends: foo < 1 && >0.7, quux < 1
+  exposed-modules: Foo
+|]
+
+caseMultipleOtherModulesWithImportFields2 :: TestTree
+caseMultipleOtherModulesWithImportFields2 =
+  mkAddTest $
+    CabalAddTest
+      { catName = "add multiple other modules with capitalised import field"
+      , catConfig =
+          AddConfig
+            { cnfComponent = Right $ CLibName LMainLibName
+            , cnfAdditions = NE.fromList ["This.Dir.Mod1", "Mod3"]
+            , cnfTargetField = OtherModules
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            }
+      , catOutput =
+          [s|
+cabal-version: 2.2
+name:          dummy
+version:       0.13.0.0
+build-type:    Simple
+
+common foo
+  build-depends: bar
+  other-modules: Other
+
+library
+  Import: foo
+  other-modules: This.Dir.Mod1, Mod3
+  build-depends: foo < 1 && >0.7, quux < 1
+  exposed-modules: Foo
+|]
+      }
+  where
+    inContents =
+      [s|
+cabal-version: 2.2
+name:          dummy
+version:       0.13.0.0
+build-type:    Simple
+
+common foo
+  build-depends: bar
+  other-modules: Other
+
+library
+  Import: foo
+  build-depends: foo < 1 && >0.7, quux < 1
+  exposed-modules: Foo
+|]
+
+caseRenameDependency1 :: TestTree
+caseRenameDependency1 =
+  mkRenameTest $
+    CabalRenameTest
+      { crtName = "rename dependency 1"
+      , crtConfig =
+          RenameConfig
+            { cnfComponent = Right $ CLibName LMainLibName
+            , cnfTargetField = BuildDepends
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            , cnfRenameFrom = "base"
+            , cnfRenameTo = "relude"
+            }
+      , crtOutput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    relude >=4.15 && <5,
+    base-foo,
+    foo-base
+
+benchmark foo
+  type: exitcode-stdio-1.0
+  main-is: Main
+  build-depends: base
+|]
+      }
+  where
+    inContents =
+      [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    base >=4.15 && <5,
+    base-foo,
+    foo-base
+
+benchmark foo
+  type: exitcode-stdio-1.0
+  main-is: Main
+  build-depends: base
+|]
+
+caseRenameDependency2 :: TestTree
+caseRenameDependency2 =
+  mkRenameTest $
+    CabalRenameTest
+      { crtName = "rename dependency 2"
+      , crtConfig =
+          RenameConfig
+            { cnfComponent = Right $ CLibName LMainLibName
+            , cnfTargetField = BuildDepends
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            , cnfRenameFrom = "base"
+            , cnfRenameTo = "relude"
+            }
+      , crtOutput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    relude>=4, relude<4, relude==4.9.0.0, relude^>=4.0, relude(>4 && <5)
+|]
+      }
+  where
+    inContents =
+      [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  build-depends:
+    base>=4, base<4, base==4.9.0.0, base^>=4.0, base(>4 && <5)
+|]
+
+caseRenameExposedModule1 :: TestTree
+caseRenameExposedModule1 =
+  mkRenameTest $
+    CabalRenameTest
+      { crtName = "rename exposed module"
+      , crtConfig =
+          RenameConfig
+            { cnfComponent = Right $ CLibName LMainLibName
+            , cnfTargetField = ExposedModules
+            , cnfFields = parseCabalFileOrError inContents
+            , cnfOrigContents = inContents
+            , cnfRenameFrom = "Data.Foo"
+            , cnfRenameTo = "Data.Quux"
+            }
+      , crtOutput =
+          [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  exposed-modules: Data.Quux, Data.Foo.Bar, Data.Foo.Baz
+
+benchmark foo
+  type: exitcode-stdio-1.0
+  main-is: Main
+  exposed-modules: Data.Foo
+|]
+      }
+  where
+    inContents =
+      [s|
+name:          dummy
+version:       0.13.0.0
+cabal-version: 2.0
+build-type:    Simple
+
+library
+  exposed-modules: Data.Foo, Data.Foo.Bar, Data.Foo.Baz
+
+benchmark foo
+  type: exitcode-stdio-1.0
+  main-is: Main
+  exposed-modules: Data.Foo
+|]
+
+prettyDiff :: [Diff String] -> String
+prettyDiff =
+  unlines
+    . mapMaybe
+      ( \case
+          First xs -> Just $ '-' : xs
+          Second ys -> Just $ '+' : ys
+          Both xs _ -> Just $ ' ' : xs
+      )
+
+mkAddTest :: CabalAddTest -> TestTree
+mkAddTest cat = singleTest (catName cat) cat
+
+mkRenameTest :: CabalRenameTest -> TestTree
+mkRenameTest cat = singleTest (crtName cat) cat
+
+main :: IO ()
+main =
+  defaultMain $
+    testGroup
+      "All Unit Tests"
+      [ caseMultipleBuildDependencies1
+      , caseMultipleExposedModules1
+      , caseMultipleExposedModulesUsingSpaces
+      , caseMultipleOtherModules
+      , caseMultipleOtherModulesUsingSpaces
+      , caseMultipleOtherModulesUsingLeadingCommas
+      , caseMultipleOtherModulesUsingLeadingSpaces
+      , caseMultipleOtherModulesWithImportFields
+      , caseMultipleOtherModulesWithImportFields2
+      , caseRenameDependency1
+      , caseRenameDependency2
+      , caseRenameExposedModule1
+      ]