PHPUnit_Framework_Constraint::evaluate PHP Method

    public function evaluate($other, $description = '', $returnResult = false)
    {
        $success = false;
        if ($this->matches($other)) {
            $success = true;
        }
        if ($returnResult) {
            return $success;
        }
        if (!$success) {
            $this->fail($other, $description);
        }
    }

 protected function matches($other)
 {
     if (!$other instanceof ResponseInterface) {
         return false;
     }
     return $this->status->evaluate($other->getStatusCode(), '', true);
 }