Integrating Unit Tests

There’s been a lot of talk about TDD, Responsibility Driven Design, and what constitutes a unit test versus an integration test this week at work.  It got me thinking about the definitions.  I used to think it was very clear cut. Unit tests isolate a single class, integration test don’t.

Is the line so simple though?  What about a unit test that tests a method that uses other methods within the same class to get its work done.  Is testing the results of that method a unit test?

For example:

// Say I wanted to test the method.
String makeDeposit( String xmlData ) {
def transaction = parseRequestXml( request )
def receipt = bankBusinessObject.deposit( transaction )
return makeResponseXml( receipt )
}

To be a unit test, I should at least mock the bankBusinessObject, and should probably ask the Mock to fail my test if the deposit method isn’t called.

But, it seems that to be a true unit test for makeDeposit, I should also mock parseRequestXml and makeResponseXml. And, for the makeDeposit unit test, rather than test that you get the expected xml repsponse data given the controlled input data, just ensure that makeDeposit calls parseRequestXml to parse it, bankBuisinessObject.deposit to act on it, and makeResponseXml to marshal the results.

I did some brain storming and came up with a new classification scheme for organizing my tests.

Unit

• Macro Unit Tests – Tests isolated to a single class.  This is where you’d see testing of methods which call other methods to get some of their work done.

• Micro Unit Tests – Tests isolated to a single method.  Completely test the method in isolation, mocking as necessary.   If you work in a language like Groovy and want to unit test a method that calls or depends on other methods in the same class, mock the dependent methods individually and have the mocks fail the test if they’re not called as expected, in the order expected.  I’m not sure if that is possible in Java.  (Maybe with some sort of test harness with AOP involved to intercept the method calls during the test??)

Integration

• Standard Integration Tests – Integration tests that span other methods, classes, depend on other services, databases, etc.

• Requirements Tests – Tests for those when you want to test a specific requirement or bug fix.  Very helpful when something changes later that breaks the bug you fixed a few releases back.  Or when the customer opens a ticket asking for functionality that contradicts a previous request.

Thoughts?