OneLogin_Saml2_Response::getError PHP Method

    public function getError()
    {
        return $this->_error;
    }

 /**
  * Tests the isValid method of the OneLogin_Saml2_Response
  * Case valid sign response / sign assertion / both signed
  *
  * Strict mode will always fail due destination problem, if we manipulate it
  * the sign will fail.
  *
  * @covers OneLogin_Saml2_Response::isValid
  */
 public function testIsValidSign()
 {
     $xml = file_get_contents(TEST_ROOT . '/data/responses/signed_message_response.xml.base64');
     $response = new OneLogin_Saml2_Response($this->_settings, $xml);
     $this->assertTrue($response->isValid());
     $xml2 = file_get_contents(TEST_ROOT . '/data/responses/signed_assertion_response.xml.base64');
     $response2 = new OneLogin_Saml2_Response($this->_settings, $xml2);
     $this->assertTrue($response2->isValid());
     $xml3 = file_get_contents(TEST_ROOT . '/data/responses/double_signed_response.xml.base64');
     $response3 = new OneLogin_Saml2_Response($this->_settings, $xml3);
     $this->assertTrue($response3->isValid());
     $dom = new DOMDocument();
     $dom->loadXML(base64_decode($xml));
     $dom->firstChild->firstChild->nodeValue = 'https://example.com/other-idp';
     $xml4 = base64_encode($dom->saveXML());
     $response4 = new OneLogin_Saml2_Response($this->_settings, $xml4);
     $this->assertFalse($response4->isValid());
     $this->assertEquals('Reference validation failed', $response4->getError());
     $dom2 = new DOMDocument();
     $dom2->loadXML(base64_decode($xml2));
     $dom2->firstChild->firstChild->nodeValue = 'https://example.com/other-idp';
     $xml5 = base64_encode($dom2->saveXML());
     $response5 = new OneLogin_Saml2_Response($this->_settings, $xml5);
     $this->assertTrue($response5->isValid());
     $dom3 = new DOMDocument();
     $dom3->loadXML(base64_decode($xml3));
     $dom3->firstChild->firstChild->nodeValue = 'https://example.com/other-idp';
     $xml6 = base64_encode($dom3->saveXML());
     $response6 = new OneLogin_Saml2_Response($this->_settings, $xml6);
     $this->assertFalse($response6->isValid());
     $this->assertEquals('Reference validation failed', $response6->getError());
 }