Test suite
As this is a bookprerequisites:test suite" about legacy applications, it would be the height of optimism to expect that the codebase has a suite of unit tests. Most legacy applications, especially include-oriented, page-based applications, are highly resistant to unit tests. There are no units to test, only a spaghetti mess of tightly coupled functionality.
And yet it is possible to test a legacy application. The key here is not to test what the system units ought to do, but what the system as a whole already does. The criteria for a successful test is that the system generates the same output after a change as it did before that change. This kind of test is called a characterization test.
It is not in the scope of this book to discuss ...
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