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。

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.

这取决于您所处的应用程序开发生命周期的哪个阶段。

If you've been at development for a while and have a lot of implemented code already and are just now realizing that you need to think about code coverage then you have to check your current coverage (if it exists) and then use that baseline to set milestones each sprint (or an average rise over a period of sprints), which means taking on code debt while continuing to deliver end user value (at least in my experience the end user doesn't care one bit if you've increased test coverage if they don't see new features).

根据你的领域，达到95%并不是不合理的，但我不得不说，平均而言，你将看到的平均情况是85%到90%。

我更喜欢做BDD，它使用自动化验收测试、可能还有其他集成测试和单元测试的组合。对我来说，问题是自动化测试套件作为一个整体的目标覆盖率应该是多少。

That aside, the answer depends on your methodology, language and testing and coverage tools. When doing TDD in Ruby or Python it's not hard to maintain 100% coverage, and it's well worth doing so. It's much easier to manage 100% coverage than 90-something percent coverage. That is, it's much easier to fill coverage gaps as they appear (and when doing TDD well coverage gaps are rare and usually worth your time) than it is to manage a list of coverage gaps that you haven't gotten around to and miss coverage regressions due to your constant background of uncovered code.

答案也取决于项目的历史。我发现上述方法只适用于从一开始就以这种方式管理的项目。我已经极大地改进了大型遗留项目的覆盖率，这样做是值得的，但是我从来没有发现回过头去填补每个覆盖率空白是可行的，因为旧的未经测试的代码不能很好地理解，不能正确和快速地完成这些工作。

代码覆盖率很好，但功能覆盖率更好。我不喜欢把我写的每一行都写一遍。但是我相信编写100%的测试覆盖我想要提供的所有功能(即使是我自己带来的额外的很酷的功能，这些功能在会议中没有讨论)。

我不关心我的代码是否会在测试中被覆盖，但我关心的是我是否会重构我的代码并最终具有不同的行为。因此，100%的功能覆盖率是我的唯一目标。

许多商店不看重测试的价值，所以如果你高于零，至少有一些价值的升值——所以可以说非零并不是坏事，因为许多仍然是零。

在。net世界中，人们经常引用80%作为合理的。但题目说的是溶液水平。我更喜欢在项目级别进行度量:如果有Selenium等或手动测试，那么UI项目的30%可能就可以了，数据层项目的20%可能就可以了，但是对于业务规则层(如果不是完全必要的话)，95%以上可能是可以实现的。因此，总体覆盖率可能是60%，但关键业务逻辑可能更高。

我也听过这样的话:追求100%，你就能达到80%;但是，立志达到80%，你就会达到40%。

底线:应用80:20规则，让应用程序的bug计数来指导你。