Unit Testing without Assertions

Question

Occasionally I come accross a unit test that doesn\'t Assert anything. The particular example I came across this morning was testing that a log file got written to when a co

Answer 1

In some sense, you are making an implicit assertion - that the code doesn't throw an exception. Of course it would be more valuable to actually grab the file and find the appropriate line, but I suppose something's better than nothing.

Answer 2

These are known as smoke tests and are common. They're basic sanity checks. But they shouldn't be the only kinds of tests you have. You'd still need some kind of verification in another test.

Answer 3

If there is no assertion, it isn't a test.

Quit being lazy -- it may take a little time to figure out how to get the assertion in there, but well worth it to know that it did what you expected it to do.

Answer 4

Such a test smells. It should check that the file was written to, at least that the modified time was updated perhaps.

I've seen quite a few tests written this way that ended up not testing anything at all i.e. the code didn't work, but it didn't blow up either.

If you have some explicit requirement that the code under test doesn't throw an exception and you want to explicitly call out this fact (tests as requirements docs) then I would do something like this:

try
{
  unitUnderTest.DoWork()
}
catch
{
  Assert.Fail("code should never throw exceptions but failed with ...")
}

... but this still smells a bit to me, probably because it's trying to prove a negative.

Answer 5

It's simply a very minimal test, and should be documented as such. It only verifies that it doesn't explode when run. The worst part about tests like this is that they present a false sense of security. Your code coverage will go up, but it's illusory. Very bad odor.

Answer 6

I've seen something like this before and I think this was done just to prop up code coverage numbers. It's probably not really testing code behaviour. In any case, I agree that it (the intention) should be documented in the test for clarity.