当我认为我的代码没有经过足够的单元测试，并且我不确定接下来要测试什么时，我使用覆盖率来帮助我决定接下来要测试什么。

如果我在一个单元测试中增加覆盖率——我知道这个单元测试有价值。

这适用于未覆盖的代码，50%覆盖或97%覆盖。

85%是签入标准的一个很好的起点。

我可能会选择各种更高的发布标准——这取决于正在测试的子系统/组件的临界性。

我认为正确的代码覆盖率的最佳症状是单元测试帮助解决的具体问题的数量合理地对应于您创建的单元测试代码的大小。

Alberto Savoia的这篇散文恰好回答了这个问题(以一种非常有趣的方式!):

http://www.artima.com/forums/flat.jsp?forum=106&thread=204677

Testivus On Test Coverage Early one morning, a programmer asked the great master: “I am ready to write some unit tests. What code coverage should I aim for?” The great master replied: “Don’t worry about coverage, just write some good tests.” The programmer smiled, bowed, and left. ... Later that day, a second programmer asked the same question. The great master pointed at a pot of boiling water and said: “How many grains of rice should I put in that pot?” The programmer, looking puzzled, replied: “How can I possibly tell you? It depends on how many people you need to feed, how hungry they are, what other food you are serving, how much rice you have available, and so on.” “Exactly,” said the great master. The second programmer smiled, bowed, and left. ... Toward the end of the day, a third programmer came and asked the same question about code coverage. “Eighty percent and no less!” Replied the master in a stern voice, pounding his fist on the table. The third programmer smiled, bowed, and left. ... After this last reply, a young apprentice approached the great master: “Great master, today I overheard you answer the same question about code coverage with three different answers. Why?” The great master stood up from his chair: “Come get some fresh tea with me and let’s talk about it.” After they filled their cups with smoking hot green tea, the great master began to answer: “The first programmer is new and just getting started with testing. Right now he has a lot of code and no tests. He has a long way to go; focusing on code coverage at this time would be depressing and quite useless. He’s better off just getting used to writing and running some tests. He can worry about coverage later.” “The second programmer, on the other hand, is quite experience both at programming and testing. When I replied by asking her how many grains of rice I should put in a pot, I helped her realize that the amount of testing necessary depends on a number of factors, and she knows those factors better than I do – it’s her code after all. There is no single, simple, answer, and she’s smart enough to handle the truth and work with that.” “I see,” said the young apprentice, “but if there is no single simple answer, then why did you answer the third programmer ‘Eighty percent and no less’?” The great master laughed so hard and loud that his belly, evidence that he drank more than just green tea, flopped up and down. “The third programmer wants only simple answers – even when there are no simple answers … and then does not follow them anyway.” The young apprentice and the grizzled great master finished drinking their tea in contemplative silence.

一般来说，从我读过的几篇工程卓越最佳实践论文来看，单元测试中80%的新代码是产生最佳回报的点。如果超过这个CC%，所付出的努力就会产生更少的缺陷。这是许多大公司所采用的最佳实践。

不幸的是，这些结果大多是公司内部的，所以我没有公开的文献可供参考。

在我看来，答案是“这取决于你有多少时间”。我试着达到100%，但如果我没有在我拥有的时间内完成它，我也不会大惊小怪。

当我编写单元测试时，我戴着与开发产品代码时不同的帽子。我考虑测试的代码声称要做什么，以及可能破坏它的情况是什么。

我通常遵循以下标准或规则:

单元测试应该是关于我的代码的预期行为的一种文档形式。给定特定输入的预期输出以及它可能抛出的客户端可能想要捕获的异常(我的代码的用户应该知道什么?) 单元测试应该帮助我发现我可能还没有想到的假设条件。(如何使我的代码稳定和健壮?)

如果这两条规则不能产生100%的覆盖率，那就顺其自然吧。但是一旦我有时间，我就会分析未覆盖的块和行，并确定是否仍然存在没有单元测试的测试用例，或者是否需要重构代码以消除不必要的代码。