SAML2\Assertion::setAuthnContextDeclRef PHP Method

    public function setAuthnContextDeclRef($authnContextDeclRef)
    {
        if (!empty($this->authnContextDecl)) {
            throw new \Exception('AuthnContextDecl is already registered! May only have either a Decl or a DeclRef, not both!');
        }
        $this->authnContextDeclRef = $authnContextDeclRef;
    }

    public function testAuthnContextDeclAndRefConstraint()
    {
        $xml = <<<XML
<samlac:AuthenticationContextDeclaration xmlns:samlac="urn:oasis:names:tc:SAML:2.0:ac">
</samlac:AuthenticationContextDeclaration>
XML;
        $document = DOMDocumentFactory::fromString($xml);
        $assertion = new Assertion();
        $e = null;
        try {
            $assertion->setAuthnContextDecl(new Chunk($document->documentElement));
            $assertion->setAuthnContextDeclRef('/relative/path/to/document.xml');
        } catch (\Exception $e) {
        }
        $this->assertNotEmpty($e);
        // Try again in reverse order for good measure.
        $assertion = new Assertion();
        $e = null;
        try {
            $assertion->setAuthnContextDeclRef('/relative/path/to/document.xml');
            $assertion->setAuthnContextDecl(new Chunk($document->documentElement));
        } catch (\Exception $e) {
        }
        $this->assertNotEmpty($e);
        // Try with unmarshalling
        $xml = <<<XML
<saml:Assertion xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion"
                xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol"
                ID="_593e33ddf86449ce4d4c22b60ac48e067d98a0b2bf"
                Version="2.0"
                 IssueInstant="2010-03-05T13:34:28Z"
>
  <saml:Issuer>testIssuer</saml:Issuer>
  <saml:AuthnStatement AuthnInstant="2010-03-05T13:34:28Z">
    <saml:AuthnContext>
      <saml:AuthnContextDecl>
        <samlac:AuthenticationContextDeclaration xmlns:samlac="urn:oasis:names:tc:SAML:2.0:ac">
        </samlac:AuthenticationContextDeclaration>
      </saml:AuthnContextDecl>
      <saml:AuthnContextDeclRef>/relative/path/to/document.xml</saml:AuthnContextDeclRef>
    </saml:AuthnContext>
  </saml:AuthnStatement>
</saml:Assertion>
XML;
        $document = DOMDocumentFactory::fromString($xml);
        $e = null;
        try {
            new Assertion($document->documentElement);
        } catch (\Exception $e) {
        }
        $this->assertNotEmpty($e);
    }