Unit testing void methods?

Question

What is the best way to unit test a method that doesn't return anything? Specifically in c#.

What I am really trying to test is a method that takes a log file and parses it for specific strings. The strings are then inserted into a database. Nothing that hasn't been done before but being VERY new to TDD I am wondering if it is possible to test this or is it something that doesn't really get tested.

Answer 1

it will have some effect on an object.... query for the result of the effect. If it has no visible effect its not worth unit testing!

Answer 2

You should also check if the method throws an exception.

Answer 3

Depends on what it's doing. If it has parameters, pass in mocks that you could ask later on if they have been called with the right set of parameters.

Answer 4

As always: test what the method is supposed to do!

Should it change global state (uuh, code smell!) somewhere?

Should it call into an interface?

Should it throw an exception when called with the wrong parameters?

Should it throw no exception when called with the right parameters?

Should it ...?

Answer 5

Presumably the method does something, and doesn't simply return?

Assuming this is the case, then:

1. If it modifies the state of it's owner object, then you should test that the state changed correctly.
2. If it takes in some object as a parameter and modifies that object, then your should test the object is correctly modified.
3. If it throws exceptions is certain cases, test that those exceptions are correctly thrown.
4. If its behaviour varies based on the state of its own object, or some other object, preset the state and test the method has the correct Ithrough one of the three test methods above).

If youy let us know what the method does, I could be more specific.

Answer 6

If a method doesn't return anything, it's either one of the following

• imperative - You're either asking the object to do something to itself.. e.g change state (without expecting any confirmation.. its assumed that it will be done)
• informational - just notifying someone that something happened (without expecting action or response) respectively.

Imperative methods - you can verify if the task was actually performed. Verify if state change actually took place. e.g.

void DeductFromBalance( dAmount )

can be tested by verifying if the balance post this message is indeed less than the initial value by dAmount

Informational methods - are rare as a member of the public interface of the object... hence not normally unit-tested. However if you must, You can verify if the handling to be done on a notification takes place. e.g.

void OnAccountDebit( dAmount )  // emails account holder with info

can be tested by verifying if the email is being sent

Post more details about your actual method and people will be able to answer better.
Update: Your method is doing 2 things. I'd actually split it into two methods that can now be independently tested.

string[] ExamineLogFileForX( string sFileName );
void InsertStringsIntoDatabase( string[] );

String[] can be easily verified by providing the first method with a dummy file and expected strings. The second one is slightly tricky.. you can either use a Mock (google or search stackoverflow on mocking frameworks) to mimic the DB or hit the actual DB and verify if the strings were inserted in the right location. Check this thread for some good books... I'd recomment Pragmatic Unit Testing if you're in a crunch.
In the code it would be used like

InsertStringsIntoDatabase( ExamineLogFileForX( "c:\OMG.log" ) );

Answer 7

Test its side-effects. This includes:

• Does it throw any exceptions? (If it should, check that it does. If it shouldn't, try some corner cases which might if you're not careful - null arguments being the most obvious thing.)
• Does it play nicely with its parameters? (If they're mutable, does it mutate them when it shouldn't and vice versa?)
• Does it have the right effect on the state of the object/type you're calling it on?

Of course, there's a limit to how much you can test. You generally can't test with every possible input, for example. Test pragmatically - enough to give you confidence that your code is designed appropriately and implemented correctly, and enough to act as supplemental documentation for what a caller might expect.

Answer 8

Use Rhino Mocks to set what calls, actions and exceptions might be expected. Assuming you can mock or stub out parts of your method. Hard to know without knowing some specifics here about the method, or even context.