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I am writing this HOWTO because, in my opinion, JUnit is very simple and easy to learn, but there is no tutorial or HOWTO out there which is

The tutorials that I used to learn JUnit spent about 80% of my time learning the program that was to be tested as an example, and the resultant tutorial therefore took five times longer to digest than it should have. There is no need to learn to understand somebody else's data structures just to learn JUnit. If you have an hour to learn to use a terrific product, then proceed.

Email me at blaine.simpson@admc.com.

JUnit is a program used to perform unit testing of virtually any software. JUnit testing is accomplished by writing test cases using Java, compiling these test cases and running the resultant classes with a JUnit Test Runner.

I will explain a teensy bit about software and unit testing in general. What and how much to test depends on how important it is to know that the tested software works right, in relation to how much time you are willing to dedicate to testing. Since you are reading this, then for some reason you have decided to dedicate at least some time to unit testing.

As an example, I'm currently developing an SMTP server. An SMTP server needs to handle email addresses of the format specified in RFC documents. To be confident that my SMTP server complies with the RFC, I need to write a test case for each allowable email address type specified in the RFC. If the RFC says that the character "#" is prohibited, then I should write a test case that sends an address with "#" and verifies that the SMTP server rejects it. You don't need to have a formal specification document to work from. If I wasn't aiming for compliance, I could just decide that it's good enough if my server accepts email addresses consisting only of letters, numbers and "@", and I don't care about whether other addresses succeed or fail.

Another important point to understand is that, everything is better if you make your tests before you implement the features. For my SMTP server, I did some prototyping first to make sure that my design will work, but I did not attempt to satsify my requirements with that prototype. I am now writing up my test cases and running them against existing SMTP server implementations (like Sendmail). When I get to the implementation stage, my work will be extremely well defined. Once my implementation satisfies all of the unit tests, just like Sendmail does, then my implementation will be completed. At that point, I'll start working on new requirements to surpass the abilities of Sendmail and will work up those tests as much as possible before starting the second implementation cycle. (If you don't have an available test target, then there sometimes comes a point where the work involved in making dummy test target isn't worth the trouble... so you just develop the test cases as far as you can until your application is ready).

Everything I've said so far has to do with unit testing, not JUnit specifically. Now on to JUnit...