There are several flaws in this argument. First, no other type of test proves that the application, running more or less as it would in production, delivers the business value its users are expecting. Unit and component tests do not test user scenarios, and are thus incapable of finding the kinds of defects that appear when users put the application through a series of states in the course of interacting with it. Acceptance tests are designed exactly for this. They are also great at catching threading problems, emergent behavior in event-driven applications, and other classes of bugs caused by
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