Steve Loughran expresses dislike for mocking in tests because mock code reflects assumptions rather than reality. Any changes to the real code can break the tests, leading to false positives. Test failures are often "fixed" by editing the test or mock code, which could hide real problems. He proposes avoiding mock tests and instead adding functional tests against real infrastructure with fault injection for integration testing.

1. Steve Loughran
stevel@hortonworks.com
@steveloughran
I hate mocking

5. when(mockClient
.initiateMultipartUpload(any(InitiateMultipartUploadRequest.class)))
.thenAnswer(new Answer<InitiateMultipartUploadResult>() {
@Override
public InitiateMultipartUploadResult answer(
InvocationOnMock invocation) throws Throwable {
LOG.debug("initiateMultipartUpload for {}", mockClient);
synchronized (lock) {
if (results.requests.size() == errors.failOnInit) {
if (errors.recover) errors.failOnInit(-1);
throw new AmazonClientException("Fail on init " + results.requests.size());
}
String uploadId = UUID.randomUUID().toString();
results.requests.put(uploadId, invocation.getArgumentAt(
0, InitiateMultipartUploadRequest.class));
results.uploads.add(uploadId);
return newResult(results.requests.get(uploadId), uploadId);
}
}
});

6. ⬢ Mock code reflects our assumptions about system behaviour
⬢ Doesn't verify that the caller would work against real service
⬢ Any change in real code breaks the tests: false positives
⬢ Test failures often "fixed" by editing test/mock
... which could hide real problems
Why bother? It's high-maintenance suffering

8. Proposed
⬢ Avoid mock tests
⬢ Add functional tests against real infrastructure
⬢ Embed fault injection ability into functional code
⬢ Use for integration testing