Organizing unit test within a test class

Question

Suppose I have several unit tests in a test class ([TestClass] in VSUnit in my case). I'm trying to test just one thing in each test (doesn't mean just one Assert though). Imagine there's one test (e.g. Test_MethodA() ) that tests a method used in other tests as well. I do not want to put an assert on this method in other tests that use it to avoid duplicity/maintainability issues so I have the assert in only this one test. Now when this test fails, all tests that depend on correct execution of that tested method fail as well. I want to be able to locate the problem faster so I want to be somehow pointed to Test_MethodA. It would e.g. help if I could make some of the tests in the test class execute in a particular order and when they fail I'd start looking for cause of the failure in the first failing test. Do you have any idea how to do this?

Edit: By suggesting that a solution would be to execute the tests in a particular order I have probably went too far and in the wrong direction. I don't care about the order of the tests. It's just that some of the tests will always fail if a prequisite isn't valid. E.g. I have a test class that tests a DAO class (ok, probably not a UNIT test, but there's logic in the database stored procedures that needs to be tested but that's not the point here I think). I need to insert some records into a table in order to test that a method responsible for retrieving the records (let's call it GetAll()) gets them all in the correct order e.g. I do the insert by using a method on the DAO class. Let's call it Insert(). I have tests in place that verify that the Insert() method works as expected. Now I want to test the GetAll() method. In order to get the database in a desired state I use the Insert() method. If Insert() doesn't work, most tests for GetAll() will fail. I'd prefer to mark the tests that can't pass because Insert() doesn't work as inconclusive rather than failed. It would ease finding the cause of the problem if I know which method/test to look into first.

Answer 1

See the following thread.

Answer 2

I'm afraid you can't do this. The only solution is to redesign your code and break it up into smaller methods so that unit tests can call these one by one. Of course this isn't always desirable.

With Visual Studio you can order your tests: see here. But I'd like to advise you to stay away from this technique as much as possible: unit tests are meant to be run anywhere, anytime and in every order.

EDIT: why is this a problem for you? All failing tests point to the same method anyway...

Answer 3

You can't (and shouldn't) execute unit tests in a specific order. The underlying reason for this is to prevent Interacting Tests - I realize that your motivation for requesting such a feature is different, but that's the reason why unit test frameworks don't allow you to order tests. In fact, last time I checked, xUnit.net even randomizes the order.

One could argue that the fact that some of your tests depend on a different method call on the same class is a symptom of tight coupling, but that's not always the case (state machines come to mind).

However, if possible, consider using a Back Door instead of the other method in question.

If you can't do either that or decouple the interdependency (e.g. by making the first method virtual and using the Extract and Override technique), you will have to live with it.

Here's an example:

public class MyClass
{
    public virtual void FirstMethod() { // do something... }

    public void SecondMethod() {}
}

Since FirstMethod is virtual, you can derive from MyClass and override its behavior. You can also use a dynamic mock to do that for you. With Moq, it would look like this:

var sutStub = new Mock<MyClass>();
// by default, Moq overrides all virtual methods without calling base

// Now invoke both methods in sequence:
sutStub.Object.FirstMethod(); // overriden by Moq, so it does nothing
sutSutb.Object.SecondMethod();

Answer 4

I think I would indeed have the assertion on the method_A() result in every tests relying on its result, even if this introduces some duplication. Then I would use the assertion message to point to the method_A() failure.

assert("method_A() returned true", true, rc);

Perhaps will I end extracting the method_A() call and the assertion into an helper function to remove the duplication.

Now let's imagine method_A() queries an object and returns it, or NULL when no object is found. Then this assertion is a guard ; and it is necessary with languages suchas C, C++ that do not have NullPointerException.