Add "letters" assertion for Unicode letters

README.md

@@ -10,7 +10,7 @@ This library contains efficient assertions to test the input and output of
 your methods. With these assertions, you can greatly reduce the amount of coding
 needed to write a safe implementation.
 
-All assertions in the [`Assert`] class throw an `\InvalidArgumentException` if 
+All assertions in the [`Assert`] class throw an `\InvalidArgumentException` if
 they fail.
 
 FAQ
@@ -22,21 +22,21 @@ This library is heavily inspired by Benjamin Eberlei's wonderful [assert package
 but fixes a usability issue with error messages that can't be fixed there without
 breaking backwards compatibility.
 
-This package features usable error messages by default. However, you can also 
+This package features usable error messages by default. However, you can also
 easily write custom error messages:
 
 ```
 Assert::string($path, 'The path is expected to be a string. Got: %s');
 ```
 
-In [beberlei/assert], the ordering of the `%s` placeholders is different for 
-every assertion. This package, on the contrary, provides consistent placeholder 
+In [beberlei/assert], the ordering of the `%s` placeholders is different for
+every assertion. This package, on the contrary, provides consistent placeholder
 ordering for all assertions:
 
 * `%s`: The tested value as string, e.g. `"/foo/bar"`.
 * `%2$s`, `%3$s`, ...: Additional assertion-specific values, e.g. the
   minimum/maximum length, allowed values, etc.
-  
+
 Check the source code of the assertions to find out details about the additional
 available placeholders.
 
@@ -69,11 +69,11 @@ If you create an employee with an invalid ID, an exception is thrown:
 
 ```php
 new Employee('foobar');
-// => InvalidArgumentException: 
+// => InvalidArgumentException:
 //    The employee ID must be an integer. Got: string
 
 new Employee(-10);
-// => InvalidArgumentException: 
+// => InvalidArgumentException:
 //    The employee ID must be a positive integer. Got: -10
 ```
 
@@ -143,6 +143,7 @@ Method                                              | Description
 `endsWith($value, $suffix, $message = '')`          | Check that a string has a suffix
 `regex($value, $pattern, $message = '')`            | Check that a string matches a regular expression
 `notRegex($value, $pattern, $message = '')`         | Check that a string does not match a regular expression
+`unicodeLetters($value, $message = '')`             | Check that a string contains Unicode letters only
 `alpha($value, $message = '')`                      | Check that a string contains letters only
 `digits($value, $message = '')`                     | Check that a string contains digits only
 `alnum($value, $message = '')`                      | Check that a string contains letters and digits only

src/Assert.php

@@ -69,6 +69,7 @@
  * @method static void nullOrEndsWith($value, $suffix, $message = '')
  * @method static void nullOrRegex($value, $pattern, $message = '')
  * @method static void nullOrNotRegex($value, $pattern, $message = '')
+ * @method static void nullOrUnicodeLetters($value, $message = '')
  * @method static void nullOrAlpha($value, $message = '')
  * @method static void nullOrDigits($value, $message = '')
  * @method static void nullOrAlnum($value, $message = '')
@@ -149,6 +150,7 @@
  * @method static void allEndsWith($values, $suffix, $message = '')
  * @method static void allRegex($values, $pattern, $message = '')
  * @method static void allNotRegex($values, $pattern, $message = '')
+ * @method static void allUnicodeLetters($values, $message = '')
  * @method static void allAlpha($values, $message = '')
  * @method static void allDigits($values, $message = '')
  * @method static void allAlnum($values, $message = '')
@@ -719,6 +721,18 @@ public static function notRegex($value, $pattern, $message = '')
         }
     }
 
+    public static function unicodeLetters($value, $message = '')
+    {
+        static::string($value);
+
+        if (!preg_match('/^\p{L}+$/u', $value)) {
+            static::reportInvalidArgument(sprintf(
+                $message ?: 'Expected a value to contain only Unicode letters. Got: %s',
+                static::valueToString($value)
+            ));
+        }
+    }
+
     public static function alpha($value, $message = '')
     {
         $locale = setlocale(LC_CTYPE, 0);

tests/AssertTest.php

@@ -287,6 +287,13 @@ public function getTests()
             array('notRegex', array('abcd', '{^ab}'), false),
             array('notRegex', array('abcd', '{^bc}'), true),
             array('notRegex', array('', '{^bc}'), true),
+            array('unicodeLetters', array('abcd'), true),
+            array('unicodeLetters', array('ᴁڅਘธブ乶'), true),
+            array('unicodeLetters', array('ȁȄ'), true),
+            array('unicodeLetters', array('ȁ1Ȅ'), false),
+            array('unicodeLetters', array('©'), false),
+            array('unicodeLetters', array('🙁'), false),
+            array('unicodeLetters', array(''), false),
             array('alpha', array('abcd'), true),
             array('alpha', array('ab1cd'), false),
             array('alpha', array(''), false),