diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,19 @@
 # Changelog
 All notable changes to the `align-equal` project will be documented in this file.
 
+## [1.0.1.0] - 2025-04-03
+
+### Added
+- Added a test suite using HSpec (`test/Spec.hs`) to validate core functions (`prefixLength`, `adjustLine`, `adjustText`).
+
+### Changed
+- Improved `adjustText` function:
+  - Now returns the original text unchanged if it's empty or contains no lines with `'='`.
+  - Updated function documentation and doctests to reflect this behavior.
+
+### Removed
+- Removed an unnecessary `newText` binding in `adjustText` for cleaner logic.
+
 ## [1.0.0] - 2025-03-31
 
 ### Changed:
diff --git a/align-equal.cabal b/align-equal.cabal
--- a/align-equal.cabal
+++ b/align-equal.cabal
@@ -1,6 +1,6 @@
 cabal-version: 3.0
 name: align-equal
-version: 1.0.0.0
+version: 1.0.1.0
 license: MIT
 license-file: LICENSE
 author: Joonkyu Park (based on original work by Gabriella Gonzalez)
@@ -41,4 +41,17 @@
     text >=2.0.2 && <2.1,
 
   hs-source-dirs: src
+  default-language: Haskell2010
+
+test-suite your-project-test
+  type: exitcode-stdio-1.0
+  hs-source-dirs: test
+  main-is: Spec.hs
+  build-depends:
+    align-equal,
+    base,
+    hspec,
+    safe,
+    text,
+
   default-language: Haskell2010
diff --git a/src/Data/Text/AlignEqual.hs b/src/Data/Text/AlignEqual.hs
--- a/src/Data/Text/AlignEqual.hs
+++ b/src/Data/Text/AlignEqual.hs
@@ -57,17 +57,23 @@
 -- | Processes multi-line text to align all '=' signs across lines.
 -- It adjusts the prefix length of each line to match the maximum prefix length.
 -- If a line does not contain '=', it will be left as-is.
+-- If the input is empty or contains no lines with '=', it is returned unchanged.
 --
 -- >>> adjustText "key=value\na=b"
 -- "key=value\na  =b"
 -- >>> adjustText "x=y\nlong=var"
 -- "x   =y\nlong=var"
+-- >>> adjustText ""
+-- ""
 adjustText
   :: Text
   -- ^ The input text (possibly multi-line)
   -> Text
-  -- ^ The aligned text
-adjustText oldText = newText
+  -- ^ The aligned text, or the original text if no '=' is found
+adjustText oldText
+  | T.null oldText = oldText
+  | null newLines = oldText
+  | otherwise = T.intercalate "\n" newLines
   where
     oldLines = T.lines oldText
 
@@ -81,5 +87,3 @@
           []
         Just desiredPrefixLength ->
           map (adjustLine desiredPrefixLength) oldLines
-
-    newText = T.unlines newLines
diff --git a/test/Spec.hs b/test/Spec.hs
new file mode 100644
--- /dev/null
+++ b/test/Spec.hs
@@ -0,0 +1,45 @@
+{-# LANGUAGE OverloadedStrings #-}
+
+module Main where
+
+import           Data.Text            (Text)
+import qualified Data.Text            as T
+import           Data.Text.AlignEqual
+import           Test.Hspec
+
+main :: IO ()
+main = hspec spec
+
+spec :: Spec
+spec = do
+  describe "prefixLength" $ do
+    it "returns Just length for lines containing '='" $ do
+      prefixLength "key=value" `shouldBe` Just 3
+      prefixLength "a=b" `shouldBe` Just 1
+      prefixLength "foo=bar=baz" `shouldBe` Just 3
+
+    it "returns Nothing for lines without '='" $ do
+      prefixLength "noequals" `shouldBe` Nothing
+      prefixLength "" `shouldBe` Nothing
+
+  describe "adjustLine" $ do
+    it "pads the prefix to match the desired length" $ do
+      adjustLine 5 "key=value" `shouldBe` "key  =value"
+      adjustLine 3 "a=b" `shouldBe` "a  =b"
+
+    it "does not add spaces if the prefix is already at the desired length" $ do
+      adjustLine 3 "foo=bar" `shouldBe` "foo=bar"
+
+    it "handles lines without '=' correctly" $ do
+      adjustLine 5 "noequals" `shouldBe` "noequals"
+
+  describe "adjustText" $ do
+    it "aligns '=' across multiple lines" $ do
+      adjustText "key=value\na=b" `shouldBe` "key=value\na  =b"
+      adjustText "x=y\nlong=var" `shouldBe` "x   =y\nlong=var"
+
+    it "leaves lines without '=' unchanged" $ do
+      adjustText "hello\nworld" `shouldBe` "hello\nworld"
+
+    it "handles empty input correctly" $ do
+      adjustText "" `shouldBe` ""