Testing Classes - When to refactor?

I'm writing a series of automatic tests in C# using NUnit and Selenium.

Edit: I am testing an entire website, to begin I wrote three classes for the three types of members that use the website, these classes contain methods which use selenium to perform various actions by these members. These classes are then created and their methods called by my test classes with the appropriate inputs.

My question is:

Does it matter how large my test class becomes? (i.e. thousands of tests?)

When is it time to refactor my functionality classes? (25 or 50 methods, 1000 lines of code, etc)

I've been trying t开发者_如何学Goo read all I can about test design so if you have any good resources I would appreciate links.

Does it matter how large my test class becomes? (i.e. thousands of tests?)

Yes it does. Tests need to be maintained in the long term, and a huge test class is difficult to understand and maintain.

When is it time to refactor my functionality classes? (25 or 50 methods, 1000 lines of code, etc)

When you start to feel it is awkward to find a specific test case, or to browse through the tests related to a specific scenario. I don't think there is a hard limit here, just as there is no hard limit for the size of production classes or the number of methods. I personally put the limits higher for test code than for production code, because test code tends to be simpler, so the threshold where it starts to become difficult to understand is higher. But in general, a 1000 line test class with 50 test methods starts to feel too big for me.

I just recently had to work with such a test class, and I ended up partitioning it, so now I have several test classes each testing one particular method / use case of a specific class*. Some of the old tests I managed to convert into parameterized tests, and all new tests are written as paramterized tests. I found that parameterized tests make it much easier to look through the big picture, and keep all test cases in mind at once. I did this using JUnit on a Java project, but I see NUnit 2.5 now offers parameterized tests too - you should check it out.

*You may rightly ask shouldn't the class under test be refactored if we need so many test cases to cover it - yes it should, eventually. It is the largest class in our legacy app, with way too much stuff in it. But first we need to have the test cases in place :-) Btw this may apply to your class too - if you need so many test cases to cover it, it might be that the class under test is just trying to do too much, and you would be better off extracting some of its functionality into a separate class, with its own unit tests.