Added test and improved exception message

Author: mcustiel

src/Match.php

@@ -87,7 +87,7 @@ public function getSubMatchAt($index)
      */
     public function getSubMatchOrDefaultAt($index, $default = null)
     {
-        return isset($this->element[$index][0]) ? $this->element[$index][0] : $default;
+        return isset($this->element[$index]) ? $this->element[$index][0] : $default;
     }
 
     /**
@@ -113,7 +113,9 @@ public function getSubmatchOffsetAt($index)
     private function validateIndex($index)
     {
         if (! isset($this->element[$index]) || $index == 0) {
-            throw new \OutOfBoundsException('Trying to access invalid submatch index');
+            throw new \OutOfBoundsException(
+                'Trying to access invalid submatch index ' . $index . 'in match: ' . $this->getFullMatch()
+            );
         }
     }
 }

tests/unit/Test/MatchTest.php

@@ -73,6 +73,15 @@ public function shouldReturnTheInnerMatch()
         $this->assertEquals('456', $this->result->getSubMatchAt(2));
     }
 
+    /**
+     * @test
+     */
+    public function shouldReturnTheDefaultIfInnerMatchIsNotSet()
+    {
+        $this->assertEquals('potato', $this->result->getSubMatchOrDefaultAt(3, 'potato'));
+        $this->assertNull($this->result->getSubMatchOrDefaultAt(4));
+    }
+
     /**
      * @test
      * @expectedException        \OutOfBoundsException