Constraint::check() uses wrong indefinite article in error message to express the type constraint

src/JsonSchema/Constraints/Type.php

@@ -10,6 +10,7 @@
 namespace JsonSchema\Constraints;
 
 use JsonSchema\Exception\InvalidArgumentException;
+use UnexpectedValueException as StandardUnexpectedValueException;
 
 /**
  * The Type Constraints, validates an element against a given type
@@ -19,6 +20,21 @@
  */
 class Type extends Constraint
 {
+    /**
+     * @var array|string[] type wordings for validation error messages
+     */
+    static $wording = array(
+        'integer' => 'an integer',
+        'number'  => 'a number',
+        'boolean' => 'a boolean',
+        'object'  => 'an object',
+        'array'   => 'an array',
+        'string'  => 'a string',
+        'null'    => 'a null',
+        'any'     => NULL, // validation of 'any' is always true so is not needed in message wording
+        0         => NULL, // validation of a false-y value is always true, so not needed as well
+    );
+
     /**
      * {@inheritDoc}
      */
@@ -56,7 +72,15 @@ public function check($value = null, $schema = null, $path = null, $i = null)
         }
 
         if ($isValid === false) {
-            $this->addError($path, gettype($value) . " value found, but a " . $type . " is required");
+            if (!isset(self::$wording[$type])) {
+                throw new StandardUnexpectedValueException(
+                    sprintf(
+                        "No wording for %s available, expected wordings are: [%s]",
+                        var_export($type, true),
+                        implode(', ', array_filter(self::$wording)))
+                );
+            }
+            $this->addError($path, gettype($value) . " value found, but " . self::$wording[$type] . " is required");
         }
     }
 

tests/JsonSchema/Tests/Constraints/TypeTest.php

@@ -0,0 +1,76 @@
+<?php
+
+/*
+ * This file is part of the JsonSchema package.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace JsonSchema\Tests\Constraints;
+
+use JsonSchema\Constraints\Type;
+
+/**
+ * Class TypeTest
+ *
+ * @package JsonSchema\Tests\Constraints
+ * @author hakre <https://github.com/hakre>
+ */
+class TypeTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @see testIndefiniteArticleForTypeInTypeCheckErrorMessage
+     * @return array
+     */
+    public function provideIndefiniteArticlesForTypes()
+    {
+        return array(
+            array('integer', 'an',),
+            array('number', 'a',),
+            array('boolean', 'a',),
+            array('object', 'an',),
+            array('array', 'an',),
+            array('string', 'a',),
+            array('null', 'a', array(), 'array',),
+        );
+    }
+
+    /**
+     * @dataProvider provideIndefiniteArticlesForTypes
+     */
+    public function testIndefiniteArticleForTypeInTypeCheckErrorMessage($type, $wording, $value = null, $label = 'NULL')
+    {
+        $constraint = new Type();
+        $constraint->check($value, (object)array('type' => $type));
+        $this->assertTypeConstraintError("$label value found, but $wording $type is required", $constraint);
+    }
+
+    /**
+     * Helper to assert an error message
+     *
+     * @param string $expected
+     * @param Type $actual
+     */
+    private function assertTypeConstraintError($expected, Type $actual)
+    {
+        $actualErrors = $actual->getErrors();
+
+        $this->assertCount(1, $actualErrors, "Failed to assert that Type has exactly one error to assert the error message against.");
+
+        $actualError = $actualErrors[0];
+
+        $this->assertInternalType('array', $actualError, sprintf('Failed to assert that Type error is an array, %s given', gettype($actualError)));
+
+        $messageKey = 'message';
+        $this->assertArrayHasKey(
+            $messageKey, $actualError,
+            sprintf('Failed to assert that Type error has a message key %s.', var_export($messageKey, true))
+        );
+
+        $actualMessage = $actualError[$messageKey];
+
+        $this->assertEquals($expected, $actualMessage); // first equal for the diff
+        $this->assertSame($expected, $actualMessage); // the same for the strictness
+    }
+}