security: cleanup validation error reporting

Change-Id: I313bedb336ecfb4180ba0f31ad77666544ba1c10
diff --git a/tests/unit/security/certificate-fetcher-direct-fetch.t.cpp b/tests/unit/security/certificate-fetcher-direct-fetch.t.cpp
index bc134a1..183a947 100644
--- a/tests/unit/security/certificate-fetcher-direct-fetch.t.cpp
+++ b/tests/unit/security/certificate-fetcher-direct-fetch.t.cpp
@@ -216,7 +216,7 @@
 
   VALIDATE_FAILURE(this->data, "Should fail, as no interests are expected");
   BOOST_CHECK_EQUAL(this->face.sentInterests.size(), 0);
-  BOOST_CHECK(this->lastError.getCode() != ValidationError::Code::IMPLEMENTATION_ERROR);
+  BOOST_CHECK_NE(this->lastError.getCode(), ValidationError::IMPLEMENTATION_ERROR);
 }
 
 BOOST_FIXTURE_TEST_CASE(ValidateSuccessInterest, CertificateFetcherDirectFetchFixture<Cert>)