diff --git a/dotenv.cabal b/dotenv.cabal
--- a/dotenv.cabal
+++ b/dotenv.cabal
@@ -1,5 +1,5 @@
 name:                dotenv
-version:             0.1.0.8
+version:             0.1.0.9
 synopsis:            Loads environment variables from dotenv files
 homepage:            https://github.com/stackbuilders/dotenv-hs
 description:
@@ -48,7 +48,7 @@
   -- other-extensions:
   build-depends:         base >=4.5 && <4.9
                        , base-compat >= 0.4
-                       , optparse-applicative >=0.11 && <0.12
+                       , optparse-applicative >=0.12 && < 0.13
                        , parsec >= 3.1.0 && <= 3.2
                        , process
 
@@ -72,6 +72,9 @@
   type: exitcode-stdio-1.0
   hs-source-dirs: spec, src
   main-is: Spec.hs
+  other-modules:         Configuration.DotenvSpec
+                       , Configuration.Dotenv.ParseSpec
+
   build-depends:       base >=4.5 && <4.9
                        , base-compat >= 0.4
                        , parsec >= 3.1.0 && <= 3.2
diff --git a/spec/Configuration/Dotenv/ParseSpec.hs b/spec/Configuration/Dotenv/ParseSpec.hs
new file mode 100644
--- /dev/null
+++ b/spec/Configuration/Dotenv/ParseSpec.hs
@@ -0,0 +1,89 @@
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module Configuration.Dotenv.ParseSpec (spec) where
+
+import Configuration.Dotenv.Parse (configParser)
+
+import Test.Hspec (it, describe, shouldBe, Spec)
+
+import Text.Parsec (ParseError, parse)
+
+import Text.ParseErrorEq ()
+
+spec :: Spec
+spec = describe "parse" $ do
+  it "parses unquoted values" $
+    parseConfig "FOO=bar" `shouldBe` Right [("FOO", "bar")]
+
+  it "parses values with spaces around equal signs" $ do
+    parseConfig "FOO =bar" `shouldBe` Right [("FOO", "bar")]
+    parseConfig "FOO= bar" `shouldBe` Right [("FOO", "bar")]
+    parseConfig "FOO =\t bar" `shouldBe` Right [("FOO", "bar")]
+
+  it "parses double-quoted values" $
+    parseConfig "FOO=\"bar\"" `shouldBe` Right [("FOO", "bar")]
+
+  it "parses single-quoted values" $
+    parseConfig "FOO='bar'" `shouldBe` Right [("FOO", "bar")]
+
+  it "parses escaped double quotes" $
+    parseConfig "FOO=\"escaped\\\"bar\"" `shouldBe`
+    Right [("FOO", "escaped\"bar")]
+
+  it "parses empty values" $
+    parseConfig "FOO=" `shouldBe` Right [("FOO", "")]
+
+  it "does not parse if line format is incorrect" $ do
+    isLeft (parseConfig "lol$wut") `shouldBe` True
+    isLeft (parseConfig "KEY=\nVALUE") `shouldBe` True
+    isLeft (parseConfig "KEY\n=VALUE") `shouldBe` True
+
+  it "expands newlines in quoted strings" $
+    parseConfig "FOO=\"bar\nbaz\"" `shouldBe` Right [("FOO", "bar\nbaz")]
+
+  it "does not parse variables with hyphens in the name" $
+    isLeft (parseConfig "FOO-BAR=foobar") `shouldBe` True
+
+  it "parses variables with '_' in the name" $
+    parseConfig "FOO_BAR=foobar" `shouldBe` Right [("FOO_BAR", "foobar")]
+
+  it "parses variables with digits after the first character" $
+    parseConfig "FOO_BAR_12=foobar" `shouldBe` Right [("FOO_BAR_12", "foobar")]
+
+  it "allows vertical spaces after a quoted variable" $
+    parseConfig "foo='bar' " `shouldBe` Right [("foo", "bar")]
+
+  it "does not parse variable names beginning with a digit" $
+    isLeft (parse configParser "null" "45FOO_BAR=foobar") `shouldBe` True
+
+  it "strips unquoted values" $
+    parseConfig "foo=bar " `shouldBe` Right [("foo", "bar")]
+
+  it "ignores empty lines" $
+    parseConfig "\n \t  \nfoo=bar\n \nfizz=buzz" `shouldBe`
+    Right [("foo", "bar"), ("fizz", "buzz")]
+
+  it "ignores inline comments after unquoted arguments" $
+    parseConfig "FOO=bar # this is foo" `shouldBe` Right [("FOO", "bar")]
+
+  it "ignores inline comments after quoted arguments" $
+    parseConfig "FOO=\"bar\" # this is foo" `shouldBe` Right [("FOO", "bar")]
+
+  it "allows # in quoted values" $
+    parseConfig "foo=\"bar#baz\" # comment" `shouldBe`
+    Right [("foo", "bar#baz")]
+
+  it "ignores comment lines" $
+    parseConfig "\n\t \n\n # HERE GOES FOO \nfoo=bar" `shouldBe`
+    Right [("foo", "bar")]
+
+  it "doesn't allow more configuration options after a quoted value" $
+    isLeft (parse configParser "null" "foo='bar'baz='buz'") `shouldBe` True
+
+
+isLeft :: Either a b -> Bool
+isLeft ( Left _ ) = True
+isLeft _          = False
+
+parseConfig :: String -> Either ParseError [(String, String)]
+parseConfig = parse configParser "(unknown)"
diff --git a/spec/Configuration/DotenvSpec.hs b/spec/Configuration/DotenvSpec.hs
new file mode 100644
--- /dev/null
+++ b/spec/Configuration/DotenvSpec.hs
@@ -0,0 +1,55 @@
+module Configuration.DotenvSpec (spec) where
+
+import Configuration.Dotenv (load, loadFile)
+
+import Test.Hspec
+
+import System.Environment.Compat (lookupEnv, setEnv, unsetEnv)
+
+{-# ANN module "HLint: ignore Reduce duplication" #-}
+
+spec :: Spec
+spec = do
+  describe "load" $ after_ (unsetEnv "foo") $ do
+    it "loads the given list of configuration options to the environment" $ do
+      lookupEnv "foo" `shouldReturn` Nothing
+
+      load False [("foo", "bar")]
+
+      lookupEnv "foo" `shouldReturn` Just "bar"
+
+    it "preserves existing settings when overload is false" $ do
+      setEnv "foo" "preset"
+
+      load False [("foo", "new setting")]
+
+      lookupEnv "foo" `shouldReturn` Just "preset"
+
+    it "overrides existing settings when overload is true" $ do
+      setEnv "foo" "preset"
+
+      load True [("foo", "new setting")]
+
+      lookupEnv "foo" `shouldReturn` Just "new setting"
+
+  describe "loadFile" $ after_ (unsetEnv "DOTENV") $ do
+    it "loads the configuration options to the environment from a file" $ do
+      lookupEnv "DOTENV" `shouldReturn` Nothing
+
+      loadFile False "spec/fixtures/.dotenv"
+
+      lookupEnv "DOTENV" `shouldReturn` Just "true"
+
+    it "respects predefined settings when overload is false" $ do
+      setEnv "DOTENV" "preset"
+
+      loadFile False "spec/fixtures/.dotenv"
+
+      lookupEnv "DOTENV" `shouldReturn` Just "preset"
+
+    it "overrides predefined settings when overload is true" $ do
+      setEnv "DOTENV" "preset"
+
+      loadFile True "spec/fixtures/.dotenv"
+
+      lookupEnv "DOTENV" `shouldReturn` Just "true"