Are multiple asserts bad in a unit test? Even if chaining?

Question

Is there anything wrong with checking so many things in this unit test?:

ActualModel = ActualResult.AssertViewRendered()        // check 1
                          .ForView("Index")            // check 2
                          .WithViewData<List<Page>>(); // check 3

CollectionAssert.AreEqual(Expected, ActualModel);      // check 4

The primary goals of this test are to verify the right view is returned (check 2) and it contains the right data (check 4).

Would I gain anything by splitting this into multiple tests? I'm all about doing things right, but I'm not going to split things up if it doesn't have practical value.

I'm pretty new to unit testing, so be gentle.

Answer 1

It's best to stick with only one assert in each test to avoid Assertion Roulette.

If you need to set up the same scenario to test multiple conditions based on identical premises, it's better to extract the setup code to a shared helper method, and then write several tests that call this helper method.

This ensures that each test case tests only one thing.

As always, there are exceptions to this rule, but since you are new to unit testing, I would recommend that you stick with the one assertion per unit test rule until you have learned when it's okay to deviate.

Answer 2

As long as each assertion has a unique and identifying failure message you should be good and will sidestep any Assertion Roulette issues because it won't be hard to tell which test failed. Use common sense.

Answer 3

As others have pointed out, it's best to stick with one assert in each test in order to avoid losing information - if the first assert fails, you don't know whether the later ones would fail also. You have to fix the problem with less information - which might (probably will) be harder.

A very good reference is Roy Osherove's Art of Unit Testing - if you want to get started right with Unit Testing, you could do a lot worse than starting here.