Write Test Scripts at the Same Time You Code
Having stepped through your code, you need to create a more formal test program that will confirm that things do indeed work. Using a test script allows for the same test to be run again in the future, perhaps after some changes have been made. The amount of test code that you write is really a matter of judgment, but what you're trying to prove is that a path of execution works correctly and any error conditions that you would expect to be raised are raised. For critical pieces of code-the mortgage calculation algorithm for a bank, for example-it might be worthwhile to actually write the specific code a second time (preferably by someone else) and then compare results from the two. Of course, there is a 50 percent chance that if there is a discrepancy, it is in the test version of the algorithm rather than the "real" version, but this approach does provide a major confidence test. I know of a company that was so sensitive about getting the accuracy of an algorithm correct that they assigned three different developers to each code the same routine. As it happened, each piece of code produced a slightly different answer. This was beneficial because it made the analyst behind this realize that he had not nailed down the specification tight enough. This is a good example of the prototype/test scenario.