Exploratory testing is not “after-everything-else-is-done” testing. Exploratory testing can (and does) take place at any stage of testing or development.
Indeed, TDD (test-driven development) is a form of exploratory development. TDD happens in loops, in which the programmer develops a check, then develops the code to make the check pass (along with all of the previous checks), then fixes any problems that she has discovered, and then loops back to implementing a new bit of behaviour and inventing a new check.
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