如果你仅编写需要满足覆盖率的测试，你会发现 bug 。那些总是失败的代码不论怎样执行，你都肯定能发现它们。但是大多数的 bug 取决于如何执行某一行代码。例如，对于“大小差一”(off-by-one)错误的代码，只有当你执行边界测试时才会失败。只有在被零除的时候，代码才会发生被零除的错误。覆盖率足够的测试会发现这些 bug 中的一部分，全靠运气，但发现得还不够多。要发现足够多的 bug ，你必须编写其他的测试“冗余地”执行代码。
For the same reason, removing tests from a regression test suite just because they don\'t add coverage is dangerous. The point is not to cover the code; it\'s to have tests that can discover enough of the bugs that are likely to be caused when the code is changed. Unless the tests are ineptly designed, removing tests will just remove power. If they are ineptly designed, using coverage converts a big and lousy test suite to a small and lousy test suite. That\'s progress, I suppose, but it\'s addressing the wrong problem.
同样的原因，因为有些测试不能增加覆盖率而将它们从回归测试套件中去掉也是危险的。关键不是覆盖代码；而是测试那些当代码更改时容易被发现的 bug 。除非测试用例是不熟练的设计，否则去掉测试用例就是去除作用力。如果它们是不熟练的设计，可以使用覆盖率将一个大而粗劣测试用例套件转化成一个小而粗劣的测试用例套件。我想这是进步，但是与这个问题无关。[Page]
A grave danger of code coverage is that it is concrete, objective, and easy to measure. Many managers today are using coverage as a performance goal for testers. Unfortunately, a cardinal rule of management applies here: \"Tell me how a person is evaluated, and I\'ll tell you how he behaves.\" If a person is evaluated by how much coverage is achieved in a given time (or in how little time it takes to reach a particular coverage goal), that person will tend to write tests to achieve high coverage in the fastest way possible. Unfortunately, that means shortchanging careful test design that targets bugs, and it certainly means avoiding in-depth, repetitive testing of \"already covered\" code.
代码覆盖率的一个重大危险是它是具体、主观而易于衡量的。今天的许多经理都使用覆盖率作为测试员的绩效目标。不幸的是，一个重要的管理规则适用于这里：“告诉我如何评价一个人，然后我才能告诉你他的表现。”如果一个人是通过在给定的时间内覆盖了多少代码（或者是在多么少的时间内达到了特定覆盖目标）来评估的，那么那个人将倾向于以尽可能快的方式达到高覆盖率的测试。不幸的是，这将意味对以发现 bug 为目的的仔细测试设计的偷工减料，这当然也意味着避开了深层次、重复地测试“已经覆盖”的代码。
Using coverage as a test design technique works only when the testers are both designing poor tests and testing redundantly. They\'d be better off at least targeting their poor tests at new areas of code. In more normal situations, coverage as a guide to design only decreases the value of the tests or puts testers under unproductive pressure to meet unhelpful goals.
仅当测试员设计了的测试质量不高并且冗余地进行测试时，将测试度作为测试设计技巧才能起作用。至少可以让他们将这些把这些质量不高的测试转移到新的领域中。在正式的场合，覆盖率作为一个设计的指导只会减少测试的价值，或将测试员置于低效率的压力下，以达到没有用处的目标。
Coverage does play a role in testing, not as a guide to test design, but as a rough evaluation of it. After you\'ve run your tests, ask what their coverage is. If certain areas of the code have no or low coverage, you\'re sure to have tested them shallowly. If that wasn\'t intentional, you should improve the tests by rethinking their design. Coverage has told you where your tests are weak, but it\'s up to you to understand how.
覆盖率在测试中确实能起作用，但不是作为测试设计的指导，而是作为一个大致的评估。在运行完测试后，看一下它们的覆盖率是多少。如果某个领域的代码没有覆盖到或覆盖率很低，可以确定你对它们的测试很肤浅。如果不是故意那样做的，你应该考虑重新设计它们以改进测试。覆盖率告诉你测试的哪个部分是薄弱的，但如何理解则取决于你。[Page]
You might not entirely ignore coverage. You might glance at the uncovered lines of code (possibly assisted by the programmer) to discover the kinds of tests you omitted. For example, you might scan the code to determine that you undertested a dialog box\'s error handling. Having done that, you step back and think of all the user errors the dialog box should handle, not how to provoke the error checks on line 343, 354, and 399. By rethinking design, you\'ll not only execute those lines, you might also discover that several other error checks are entirely missing. (Coverage can\'t tell you how well you would have exercised needed code that was left out of the program.)
你也不能完全忽略覆盖率。你可以浏览未覆盖的代码行（可能是在程序员的辅助下）以发现你忽略的某种测试。例如，你可能浏览代码以确定你是否对某个对话框的错误处理测试不足。在完成这些之后，你翻回头应该考虑对话框应该处理的所有用户错误，而不是检查第343、354和399行的错误。通过重新思考设计，你不仅能执行那些行，而且可能会发现几个其他完全被忽略了错误。（覆盖率不能告诉你程序之外的、所需要代码的执行情况）。
There are types of coverage that point more directly to design mistakes than statement coverage does (branch coverage, for example). However, none - and not all of them put together - are so accurate that they can be used as test design techniques.
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