diff --git a/bower.json b/bower.json
index b4c32dc..f9aed89 100644
--- a/bower.json
+++ b/bower.json
@@ -20,5 +20,9 @@
   ],
   "dependencies": {
     "purescript-maybe": "^0.3.0"
+  },
+  "devDependencies": {
+    "purescript-assert": "~0.1.0",
+    "purescript-console": "~0.1.0"
   }
 }
diff --git a/docs/Data/Char.md b/docs/Data/Char.md
index c143a21..8a63047 100644
--- a/docs/Data/Char.md
+++ b/docs/Data/Char.md
@@ -26,4 +26,20 @@ fromCharCode :: Int -> Char
 
 Constructs a character from the given Unicode numeric value.
 
+#### `toLower`
+
+``` purescript
+toLower :: Char -> Char
+```
+
+Converts a character to lowercase.
+
+#### `toUpper`
+
+``` purescript
+toUpper :: Char -> Char
+```
+
+Converts a character to uppercase.
+
 
diff --git a/docs/Data/String.md b/docs/Data/String.md
index b5f4771..d9ad647 100644
--- a/docs/Data/String.md
+++ b/docs/Data/String.md
@@ -198,8 +198,9 @@ of the string for which the predicate holds.
 split :: String -> String -> Array String
 ```
 
-Returns the substrings of the first string separated along occurences
-of the second string.
+Returns the substrings of the second string separated along occurences
+of the first string.
+* `split " " "hello world" == ["hello", "world"]`
 
 #### `toCharArray`
 
diff --git a/docs/Data/String/Regex.md b/docs/Data/String/Regex.md
index 95a6150..bcc0427 100644
--- a/docs/Data/String/Regex.md
+++ b/docs/Data/String/Regex.md
@@ -115,11 +115,11 @@ See the [reference](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Refe
 #### `search`
 
 ``` purescript
-search :: Regex -> String -> Int
+search :: Regex -> String -> Maybe Int
 ```
 
-Returns the index of the first match of the `Regex` in the string, or
-`-1` if there is no match.
+Returns `Just` the index of the first match of the `Regex` in the string,
+or `Nothing` if there is no match.
 
 #### `split`
 
diff --git a/package.json b/package.json
index e129c49..2d38aab 100644
--- a/package.json
+++ b/package.json
@@ -2,7 +2,7 @@
   "private": true,
   "scripts": {
     "postinstall": "pulp dep install",
-    "build": "jshint src && jscs src && pulp build && rimraf docs && pulp docs"
+    "build": "jshint src && jscs src && pulp build && pulp test && rimraf docs && pulp docs"
   },
   "devDependencies": {
     "jscs": "^1.13.1",
diff --git a/src/Data/Char.js b/src/Data/Char.js
index b4885a6..7a929c6 100644
--- a/src/Data/Char.js
+++ b/src/Data/Char.js
@@ -14,3 +14,11 @@ exports.toCharCode = function (c) {
 exports.fromCharCode = function (c) {
   return String.fromCharCode(c);
 };
+
+exports.toLower = function (c) {
+  return c.toLowerCase();
+};
+
+exports.toUpper = function (c) {
+  return c.toUpperCase();
+};
diff --git a/src/Data/Char.purs b/src/Data/Char.purs
index 207890d..17dd992 100644
--- a/src/Data/Char.purs
+++ b/src/Data/Char.purs
@@ -3,6 +3,8 @@ module Data.Char
   ( toString
   , fromCharCode
   , toCharCode
+  , toLower
+  , toUpper
   ) where
 
 import Prelude
@@ -16,11 +18,13 @@ foreign import toCharCode :: Char -> Int
 -- | Constructs a character from the given Unicode numeric value.
 foreign import fromCharCode :: Int -> Char
 
+-- | Converts a character to lowercase.
+foreign import toLower :: Char -> Char
+
+-- | Converts a character to uppercase.
+foreign import toUpper :: Char -> Char
+
 -- | Characters fall within the Unicode range.
 instance boundedChar :: Bounded Char where
   top = fromCharCode zero
   bottom = fromCharCode 65535
-
--- | Characters can be rendered as a string with `show`.
-instance showChar :: Show Char where
-  show c = "Char " ++ show (toString c)
diff --git a/src/Data/String.js b/src/Data/String.js
index 5e47ced..bf50543 100644
--- a/src/Data/String.js
+++ b/src/Data/String.js
@@ -51,6 +51,7 @@ exports["_indexOf'"] = function (just) {
     return function (x) {
       return function (startAt) {
         return function (s) {
+          if (startAt < 0 || startAt > s.length) return nothing;
           var i = s.indexOf(x, startAt);
           return i === -1 ? nothing : just(i);
         };
@@ -75,6 +76,7 @@ exports["_lastIndexOf'"] = function (just) {
     return function (x) {
       return function (startAt) {
         return function (s) {
+          if (startAt < 0 || startAt > s.length) return nothing;
           var i = s.lastIndexOf(x, startAt);
           return i === -1 ? nothing : just(i);
         };
@@ -93,7 +95,7 @@ exports._localeCompare = function (lt) {
       return function (s1) {
         return function (s2) {
           var result = s1.localeCompare(s2);
-          return result < 0 ? lt : result > 1 ? gt : eq;
+          return result < 0 ? lt : result > 0 ? gt : eq;
         };
       };
     };
diff --git a/src/Data/String.purs b/src/Data/String.purs
index 652d077..7af4fed 100644
--- a/src/Data/String.purs
+++ b/src/Data/String.purs
@@ -33,7 +33,7 @@ module Data.String
   ) where
 
 import Prelude
-import Data.Char
+import qualified Data.Char as C
 import Data.Maybe (Maybe(..), isJust)
 import Data.Monoid (Monoid)
 import qualified Data.String.Unsafe as U
@@ -50,7 +50,7 @@ foreign import _charAt :: (forall a. a -> Maybe a)
 
 -- | Returns a string of length `1` containing the given character.
 fromChar :: Char -> String
-fromChar = toString
+fromChar = C.toString
 
 -- | Returns a string of length `1` containing the given character.
 -- | Same as `fromChar`.
diff --git a/src/Data/String/Regex.js b/src/Data/String/Regex.js
index 01e8a2e..f70bef3 100644
--- a/src/Data/String/Regex.js
+++ b/src/Data/String/Regex.js
@@ -70,9 +70,14 @@ exports["replace'"] = function (r) {
   };
 };
 
-exports.search = function (r) {
-  return function (s) {
-    return s.search(r);
+exports._search = function (just) {
+  return function (nothing) {
+    return function (r) {
+      return function (s) {
+        var result = s.search(r);
+        return result === -1 ? nothing : just(result);
+      };
+    };
   };
 };
 
diff --git a/src/Data/String/Regex.purs b/src/Data/String/Regex.purs
index 3bec5b9..d0bf1ea 100644
--- a/src/Data/String/Regex.purs
+++ b/src/Data/String/Regex.purs
@@ -104,9 +104,16 @@ foreign import replace :: Regex -> String -> String -> String
 -- | See the [reference](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace#Specifying_a_function_as_a_parameter).
 foreign import replace' :: Regex -> (String -> Array String -> String) -> String -> String
 
--- | Returns the index of the first match of the `Regex` in the string, or
--- | `-1` if there is no match.
-foreign import search :: Regex -> String -> Int
+foreign import _search :: (forall r. r -> Maybe r)
+                       -> (forall r. Maybe r)
+                       -> Regex
+                       -> String
+                       -> Maybe Int
+
+-- | Returns `Just` the index of the first match of the `Regex` in the string,
+-- | or `Nothing` if there is no match.
+search :: Regex -> String -> Maybe Int
+search = _search Just Nothing
 
 -- | Split the string into an array of substrings along occurences of the `Regex`.
 foreign import split :: Regex -> String -> Array String
diff --git a/test/Test/Data/Char.purs b/test/Test/Data/Char.purs
new file mode 100644
index 0000000..5063b74
--- /dev/null
+++ b/test/Test/Data/Char.purs
@@ -0,0 +1,27 @@
+module Test.Data.Char (testChar) where
+
+import Prelude
+import Control.Monad.Eff.Console (log)
+import Data.Char
+import Test.Assert (assert)
+
+testChar = do
+  log "toString"
+  assert $ toString 'a' == "a"
+
+  log "toCharCode"
+  assert $ toCharCode 'a' == 97
+  assert $ toCharCode '\n' == 10
+
+  log "fromCharCode"
+  assert $ fromCharCode 97 == 'a'
+  assert $ fromCharCode 10 == '\n'
+
+  log "toLower"
+  assert $ toLower 'A' == 'a'
+  assert $ toLower 'a' == 'a'
+
+  log "toUpper"
+  assert $ toUpper 'a' == 'A'
+  assert $ toUpper 'A' == 'A'
+
diff --git a/test/Test/Data/String.purs b/test/Test/Data/String.purs
new file mode 100644
index 0000000..4f43ac3
--- /dev/null
+++ b/test/Test/Data/String.purs
@@ -0,0 +1,175 @@
+module Test.Data.String (testString) where
+
+import Prelude
+import Data.Maybe
+import Control.Monad.Eff.Console (log)
+import Data.String
+import Test.Assert (assert)
+
+testString = do
+  log "charAt"
+  assert $ charAt 0 "" == Nothing
+  assert $ charAt 0 "a" == Just 'a'
+  assert $ charAt 1 "a" == Nothing
+  assert $ charAt 0 "ab" == Just 'a'
+  assert $ charAt 1 "ab" == Just 'b'
+  assert $ charAt 2 "ab" == Nothing
+
+  log "fromChar"
+  assert $ fromChar 'a' == "a"
+
+  log "singleton"
+  assert $ singleton 'a' == "a"
+
+  log "charCodeAt"
+  assert $ charCodeAt 0 "" == Nothing
+  assert $ charCodeAt 0 "a" == Just 97
+  assert $ charCodeAt 1 "a" == Nothing
+  assert $ charCodeAt 0 "ab" == Just 97
+  assert $ charCodeAt 1 "ab" == Just 98
+  assert $ charCodeAt 2 "ab" == Nothing
+
+  log "toChar"
+  assert $ toChar "" == Nothing
+  assert $ toChar "a" == Just 'a'
+  assert $ toChar "ab" == Nothing
+
+  log "null"
+  assert $ null ""
+  assert $ not (null "a")
+
+  log "uncons"
+  assert $ isNothing (uncons "")
+  assert $ case uncons "a" of
+                Nothing -> false
+                Just m -> m.head == 'a' && m.tail == ""
+  assert $ case uncons "ab" of
+                Nothing -> false
+                Just m -> m.head == 'a' && m.tail == "b"
+
+  log "takeWhile"
+  assert $ takeWhile (\c -> true) "abc" == "abc"
+  assert $ takeWhile (\c -> false) "abc" == ""
+  assert $ takeWhile (\c -> c /= 'b') "aabbcc" == "aa"
+
+  log "dropWhile"
+  assert $ dropWhile (\c -> true) "abc" == ""
+  assert $ dropWhile (\c -> false) "abc" == "abc"
+  assert $ dropWhile (\c -> c /= 'b') "aabbcc" == "bbcc"
+
+  log "stripPrefix"
+  assert $ stripPrefix "" "" == Just ""
+  assert $ stripPrefix "" "abc" == Just "abc"
+  assert $ stripPrefix "a" "abc" == Just "bc"
+  assert $ stripPrefix "!" "abc" == Nothing
+  assert $ stripPrefix "!" "" == Nothing
+
+  log "fromCharArray"
+  assert $ fromCharArray [] == ""
+  assert $ fromCharArray ['a', 'b'] == "ab"
+
+  log "contains"
+  assert $ contains "" ""
+  assert $ contains "" "abcd"
+  assert $ contains "bc" "abcd"
+  assert $ not (contains "cb" "abcd")
+
+  log "indexOf"
+  assert $ indexOf "" "" == Just 0
+  assert $ indexOf "" "abcd" == Just 0
+  assert $ indexOf "bc" "abcd" == Just 1
+  assert $ indexOf "cb" "abcd" == Nothing
+
+  log "indexOf'"
+  assert $ indexOf' "" 0 "" == Just 0
+  assert $ indexOf' "" (-1) "ab" == Nothing
+  assert $ indexOf' "" 0 "ab" == Just 0
+  assert $ indexOf' "" 1 "ab" == Just 1
+  assert $ indexOf' "" 2 "ab" == Just 2
+  assert $ indexOf' "" 3 "ab" == Nothing
+  assert $ indexOf' "bc" 0 "abcd" == Just 1
+  assert $ indexOf' "bc" 1 "abcd" == Just 1
+  assert $ indexOf' "bc" 2 "abcd" == Nothing
+  assert $ indexOf' "cb" 0 "abcd" == Nothing
+
+  log "lastIndexOf"
+  assert $ lastIndexOf "" "" == Just 0
+  assert $ lastIndexOf "" "abcd" == Just 4
+  assert $ lastIndexOf "bc" "abcd" == Just 1
+  assert $ lastIndexOf "cb" "abcd" == Nothing
+
+  log "lastIndexOf'"
+  assert $ lastIndexOf' "" 0 "" == Just 0
+  assert $ lastIndexOf' "" (-1) "ab" == Nothing
+  assert $ lastIndexOf' "" 0 "ab" == Just 0
+  assert $ lastIndexOf' "" 1 "ab" == Just 1
+  assert $ lastIndexOf' "" 2 "ab" == Just 2
+  assert $ lastIndexOf' "" 3 "ab" == Nothing
+  assert $ lastIndexOf' "bc" 0 "abcd" == Nothing
+  assert $ lastIndexOf' "bc" 1 "abcd" == Just 1
+  assert $ lastIndexOf' "bc" 2 "abcd" == Just 1
+  assert $ lastIndexOf' "cb" 0 "abcd" == Nothing
+
+  log "length"
+  assert $ length "" == 0
+  assert $ length "a" == 1
+  assert $ length "ab" == 2
+
+  log "localeCompare"
+  assert $ localeCompare "" "" == EQ
+  assert $ localeCompare "a" "a" == EQ
+  assert $ localeCompare "a" "b" == LT
+  assert $ localeCompare "b" "a" == GT
+
+  log "replace"
+  assert $ replace "b" "" "abc" == "ac"
+  assert $ replace "b" "!" "abc" == "a!c"
+  assert $ replace "d" "!" "abc" == "abc"
+
+  log "take"
+  assert $ take 0 "ab" == ""
+  assert $ take 1 "ab" == "a"
+  assert $ take 2 "ab" == "ab"
+  assert $ take 3 "ab" == "ab"
+
+  log "drop"
+  assert $ drop 0 "ab" == "ab"
+  assert $ drop 1 "ab" == "b"
+  assert $ drop 2 "ab" == ""
+  assert $ drop 3 "ab" == ""
+
+  log "count"
+  assert $ count (\c -> true) "" == 0
+  assert $ count (\c -> true) "ab" == 2
+  assert $ count (\c -> false) "ab" == 0
+  assert $ count (\c -> c == 'a') "aabbcc" == 2
+  assert $ count (\c -> c == 'b') "aabbcc" == 0
+  assert $ count (\c -> c /= 'a') "aabbcc" == 0
+  assert $ count (\c -> c /= 'b') "aabbcc" == 2
+
+  log "split"
+  assert $ split "" "" == []
+  assert $ split "" "a" == ["a"]
+  assert $ split "" "ab" == ["a", "b"]
+  assert $ split "b" "aabcc" == ["aa", "cc"]
+  assert $ split "d" "abc" == ["abc"]
+
+  log "toCharArray"
+  assert $ toCharArray "" == []
+  assert $ toCharArray "a" == ['a']
+  assert $ toCharArray "ab" == ['a', 'b']
+
+  log "toLower"
+  assert $ toLower "bAtMaN" == "batman"
+
+  log "toUpper"
+  assert $ toUpper "bAtMaN" == "BATMAN"
+
+  log "trim"
+  assert $ trim "  abc  " == "abc"
+
+  log "joinWith"
+  assert $ joinWith "" [] == ""
+  assert $ joinWith "" ["a", "b"] == "ab"
+  assert $ joinWith "--" ["a", "b", "c"] == "a--b--c"
+
diff --git a/test/Test/Data/String/Regex.purs b/test/Test/Data/String/Regex.purs
new file mode 100644
index 0000000..bcf708a
--- /dev/null
+++ b/test/Test/Data/String/Regex.purs
@@ -0,0 +1,31 @@
+module Test.Data.String.Regex (testStringRegex) where
+
+import Prelude
+import Data.Maybe
+import Control.Monad.Eff.Console (log)
+import Data.String.Regex
+import Test.Assert (assert)
+
+testStringRegex = do
+  log "regex"
+  assert $ test (regex "^a" noFlags) "abc"
+  assert $ not (test (regex "^b" noFlags) "abc")
+
+  log "match"
+  assert $ match (regex "^abc$" noFlags) "abc" == Just [Just "abc"]
+
+  log "replace"
+  assert $ replace (regex "-" noFlags) "!" "a-b-c" == "a!b-c"
+
+  log "replace'"
+  assert $ replace' (regex "-" noFlags) (\s xs -> "!") "a-b-c" == "a!b-c"
+
+  log "search"
+  assert $ search (regex "b" noFlags) "abc" == Just 1
+  assert $ search (regex "d" noFlags) "abc" == Nothing
+
+  log "split"
+  assert $ split (regex "" noFlags) "" == []
+  assert $ split (regex "" noFlags) "abc" == ["a", "b", "c"]
+  assert $ split (regex "b" noFlags) "" == [""]
+  assert $ split (regex "b" noFlags) "abc" == ["a", "c"]
diff --git a/test/Test/Data/String/Unsafe.purs b/test/Test/Data/String/Unsafe.purs
new file mode 100644
index 0000000..de9a53c
--- /dev/null
+++ b/test/Test/Data/String/Unsafe.purs
@@ -0,0 +1,18 @@
+module Test.Data.String.Unsafe (testStringUnsafe) where
+
+import Prelude
+import Control.Monad.Eff.Console (log)
+import Data.String.Unsafe
+import Test.Assert (assert)
+
+testStringUnsafe = do
+  log "charCodeAt"
+  assert $ charCodeAt 0 "ab" == 97
+  assert $ charCodeAt 1 "ab" == 98
+
+  log "charAt"
+  assert $ charAt 0 "ab" == 'a'
+  assert $ charAt 1 "ab" == 'b'
+
+  log "char"
+  assert $ char "a" == 'a'
diff --git a/test/Test/Main.purs b/test/Test/Main.purs
new file mode 100644
index 0000000..78bbcf2
--- /dev/null
+++ b/test/Test/Main.purs
@@ -0,0 +1,13 @@
+module Test.Main where
+
+import Prelude
+import Test.Data.Char
+import Test.Data.String
+import Test.Data.String.Unsafe
+import Test.Data.String.Regex
+
+main = do
+  testChar
+  testString
+  testStringUnsafe
+  testStringRegex