Code Complete: A Practical Handbook of Software Construction, Second Edition

The steps for improving your testing are similar to the steps for improving any other process. You have to know exactly what the process does so that you can vary it slightly and observe the effects of the variation. When you observe a change that has a positive effect, you modify the process so that it becomes a little better. The following sections describe how to do this with testing.

Planning to Test

One key to effective testing is planning from the beginning of the project to test. Putting testing on the same level of importance as design or coding means that time will be allocated to it, it will be viewed as important, and it will be a high-quality process. Test planning is also an element of making the testing process repeatable. If you can't repeat it, you can't improve it.

Cross-Reference

Part of planning to test is formalizing your plans in writing. To find further information on test documentation, refer to the "Additional Resources" section at the end of Chapter 32.

Retesting (Regression Testing)

Suppose that you've tested a product thoroughly and found no errors. Suppose that the product is then changed in one area and you want to be sure that it still passes all the tests it did before the change that the change didn't introduce any new defects. Testing designed to make sure the software hasn't taken a step backward, or "regressed," is called "regression testing."

It's nearly impossible to produce a high-quality software product unless you can systematically retest it after changes have been made. If you run different tests after each change, you have no way of knowing for sure that no new defects have been introduced. Consequently, regression testing must run the same tests each time. Sometimes new tests are added as the product matures, but the old tests are kept too.

Automated Testing

Benefits of test automation include the following:

• An automated test has a lower chance of being wrong than a manual test.

• Once you automate a test, it's readily available for the rest of the project with little incremental effort on your part.

• If tests are automated, they can be run frequently to see whether any code checkins have broken the code. Test automation is part of the foundation of test-intensive practices, such as the daily build and smoke test and Extreme Programming.

• Automated tests improve your chances of detecting any given problem at the earliest possible moment, which tends to minimize the work needed to diagnose and correct the problem.

• Automated tests provide a safety net for large-scale code changes because they increase your chance of quickly detecting defects inserted during the modifications.

• Automated tests are especially useful in new, volatile technology environments because they flush out changes in the environments sooner rather than later.

  Cross-Reference

  For more on the relationship between technology maturity and development practices, see Section 4.3, "Your Location on the Technology Wave."