Testing, Testing and Testing

You hear it in real estate: location, location, location.  You hear it (not as much) in software: test, test, test.  However, in software the tests are all different.

A recent project that I'm on involves a venerable app with as much technical debt as the US Government... and we need to add a feature.  Solution: tests, tests and tests.  More specifically if you don't know the different kinds of tests:

• Good old Unit Testing, easy to implement and understand, unless...
• You are getting used to mock objects (e.g. JMock or Mockito)
• You are testing database functionality and are new to DBUnit
• You are testing a web app or Servlet and are new to HttpUnit
• You're confusing unit testing (ONE module) with integration testing (multiple modules)
• Example: testing your Data Access Layer (DAL) with a dummy DB, like a local HSQL
• Integration Testing, usually implemented with a framework that ends in "Unit" so it's easily confused with unit testing.  Integration testing integrates two or more components, everything from two classes to the entire app with a dummy DB.  Due to this you can have multiple levels of integration tests, each testing more modules together.  Examples include:
• Testing a servlet in HttpUnit's ServletUnit instead of your actual web container
• Testing your DAL with an "actual" database (whatever actual means to your project)
• Testing a fully created Spring bean with the real beans injected instead of mocks
• System Testing, this is tests of the entire system
• QA usually conducts manual system tests
• There can be automated ones as well with things like Selenium
• As an example for a web app, using a supported browser to use the app in the final web container and using the real database.

There is of course, much more to software testing, but these three are usually a good start.  Heck, in many organizations / projects even using unit testing is new to people.  Like Regan said: trust, but verify.

PS: There's a good post at EvilTester with a more philosophical approach to testing.