diff --git a/src/ArrayDiffMultidimensional.php b/src/ArrayDiffMultidimensional.php
index b370674..f72b5d0 100644
--- a/src/ArrayDiffMultidimensional.php
+++ b/src/ArrayDiffMultidimensional.php
@@ -6,18 +6,25 @@ class ArrayDiffMultidimensional
 {
 
     /**
-     * Returns an array with the differences between $array1 and $array2
-     *
-     * @param array $aArray1
-     * @param array $aArray2
+     * Returns an array with items that are present in first array,
+     * but not in the second one. If second argument is not
+     * array first array is returned.
+     * @param mixed $array1
+     * @param mixed $array2
      * @return array
+     * @internal param array $aArray1
+     * @internal param array $aArray2
      */
     public static function compare($array1, $array2)
     {
         $result = array();
 
+        if (!is_array($array2)) {
+            return $array1;
+        }
+
         foreach ($array1 as $key => $value) {
-            if (!is_array($array2) || !array_key_exists($key, $array2)) {
+            if (!array_key_exists($key, $array2)) {
                 $result[$key] = $value;
                 continue;
             }
diff --git a/tests/ArrayCompareTest.php b/tests/ArrayCompareTest.php
index b7d5729..bc19128 100644
--- a/tests/ArrayCompareTest.php
+++ b/tests/ArrayCompareTest.php
@@ -6,76 +6,133 @@
 
 class ArrayCompareTest extends \PHPUnit_Framework_TestCase
 {
-	protected $diff;
-
-	public function setUp()
-	{
-		$this->diff = new ArrayDiffMultidimensional();
-	}
-
-	/** @test */
-	public function returnsAnArray()
-	{
-		$this->assertTrue( is_array($this->diff->compare([],[])) );
-	}
-
-	/** @test */
-	public function DetectsTheDifferenceOnStringValue()
-	{
-		$old = [
-			'a' => 'b',
-			'c' => uniqid(),
-		];
-
-		$new = [
-			'a' => 'b',
-			'c' => uniqid(),
-		];
-
-		$this->assertEquals( count($this->diff->compare($new,$old)), 1 );
-		$this->assertTrue( isset($this->diff->compare($new,$old)['c']) );
-	}
-
-	/** @test */
-	public function DetectsChangeFromStringToArray()
-	{
-		$new = [
-			'a' => 'b',
-			'c' => [
-				'd' => uniqid(),
-				'e' => uniqid(),
-			],
-		];
-
-		$old = [
-			'a' => 'b',
-			'c' => uniqid(),
-		];
-
-		$this->assertEquals( count($this->diff->compare($new,$old)), 1 );
-		$this->assertTrue( is_array($this->diff->compare($new,$old)['c']) );
-	}
-
-	/** @test */
-	public function DetectsChangesOnNestedArrays()
-	{
-		$new = [
-			'a' => 'b',
-			'c' => [
-				'd' => 'e',
-				'f' => uniqid(),
-			],
-		];
-
-		$old = [
-			'a' => 'b',
-			'c' => [
-				'd' => 'e',
-				'f' => uniqid(),
-			],
-		];
-
-		$this->assertEquals( count($this->diff->compare($new,$old)), 1 );
-		$this->assertTrue( isset($this->diff->compare($new,$old)['c']['f']) );
-	}
+    protected $diff;
+
+    public function setUp()
+    {
+        $this->diff = new ArrayDiffMultidimensional();
+    }
+
+    /** @test */
+    public function returnsAnArray()
+    {
+        $this->assertTrue(is_array($this->diff->compare([], [])));
+    }
+
+    /** @test */
+    public function DetectsTheDifferenceOnStringValue()
+    {
+        $old = [
+            'a' => 'b',
+            'c' => uniqid(),
+        ];
+
+        $new = [
+            'a' => 'b',
+            'c' => uniqid(),
+        ];
+
+        $this->assertEquals(count($this->diff->compare($new, $old)), 1);
+        $this->assertTrue(isset($this->diff->compare($new, $old)['c']));
+    }
+
+    /** @test */
+    public function DetectsChangeFromStringToArray()
+    {
+        $new = [
+            'a' => 'b',
+            'c' => [
+                'd' => uniqid(),
+                'e' => uniqid(),
+            ],
+        ];
+
+        $old = [
+            'a' => 'b',
+            'c' => uniqid(),
+        ];
+
+        $this->assertEquals(count($this->diff->compare($new, $old)), 1);
+        $this->assertTrue(is_array($this->diff->compare($new, $old)['c']));
+    }
+
+    /** @test */
+    public function DetectsChangesOnNestedArrays()
+    {
+        $new = [
+            'a' => 'b',
+            'c' => [
+                'd' => 'e',
+                'f' => uniqid(),
+            ],
+        ];
+
+        $old = [
+            'a' => 'b',
+            'c' => [
+                'd' => 'e',
+                'f' => uniqid(),
+            ],
+        ];
+
+        $this->assertEquals(count($this->diff->compare($new, $old)), 1);
+        $this->assertTrue(isset($this->diff->compare($new, $old)['c']['f']));
+    }
+
+    /** @test */
+    public function BeAwareThatThisArrayAreEquals()
+    {
+        $new = [
+            'a' => 'b',
+            'c' => [
+                'd' => 'e',
+            ],
+        ];
+
+        $old = [
+            'a' => 'b',
+            'c' => [
+                'd' => 'e',
+                'f' => uniqid(),
+            ],
+        ];
+
+        $this->assertNotEquals(1, count($this->diff->compare($new, $old)));
+    }
+
+
+    /** @test */
+    public function SecondArgumentIsNotArray()
+    {
+        $old = [
+            'a' => 'b',
+            'c' => [
+                'd' => 'e',
+                'ff' => [
+                    'test'
+                ]
+            ],
+        ];
+
+        $new = 100;
+
+        $this->assertEquals($old, $this->diff->compare($old, $new));
+    }
+
+    /**
+     * @test
+     * @expectedException \PHPUnit_Framework_Error
+     */
+    public function FirstArgumentIsNotArray()
+    {
+        $old = null;
+        $new = [
+            'a' => 'b',
+            'c' => [
+                'd' => 'e',
+            ],
+        ];
+
+        $this->assertEquals($new, $this->diff->compare($old, $new));
+    }
 }
\ No newline at end of file