摘自Code Complete (Wikipedia):

8 Defensive Programming 8.2 Assertions An assertion is code that’s used during development—usually a routine or macro—that allows a program to check itself as it runs. When an assertion is true, that means everything is operating as expected. When it’s false, that means it has detected an unexpected error in the code. For example, if the system assumes that a customer-information file will never have more than 50,000 records, the program might contain an assertion that the number of records is lessthan or equal to 50,000. As long as the number of records is less than or equal to 50,000, the assertion will be silent. If it encounters more than 50,000 records, however, it will loudly “assert” that there is an error in the program. Assertions are especially useful in large, complicated programs and in high reliability programs. They enable programmers to more quickly flush out mismatched interface assumptions, errors that creep in when code is modified, and so on. An assertion usually takes two arguments: a boolean expression that describes the assumption that’s supposed to be true and a message to display if it isn’t. (…) Normally, you don’t want users to see assertion messages in production code; assertions are primarily for use during development and maintenance. Assertions are normally compiled into the code at development time and compiled out of the code for production. During development, assertions flush out contradictory assumptions, unexpected conditions, bad values passed to routines, and so on. During production, they are compiled out of the code so that the assertions don’t degrade system performance.

您应该使用Debug。断言来测试程序中的逻辑错误。编译器只能通知您语法错误。因此，您肯定应该使用Assert语句来测试逻辑错误。比如测试一个销售汽车的项目，只有蓝色的宝马可以得到15%的折扣。编译器不能告诉你你的程序在执行这个操作时逻辑上是否正确，但是assert语句可以。

John Robbins在《调试Microsoft . net 2.0应用程序》一书中有一大节是关于断言的。他的主要观点是:

Assert liberally. You can never have too many assertions. Assertions don't replace exceptions. Exceptions cover the things your code demands; assertions cover the things it assumes. A well-written assertion can tell you not just what happened and where (like an exception), but why. An exception message can often be cryptic, requiring you to work backwards through the code to recreate the context that caused the error. An assertion can preserve the program's state at the time the error occurred. Assertions double as documentation, telling other developers what implied assumptions your code depends on. The dialog that appears when an assertion fails lets you attach a debugger to the process, so you can poke around the stack as if you had put a breakpoint there.

PS:如果你喜欢《代码完成》，我推荐你继续阅读这本书。我买这本书是为了学习如何使用WinDBG和转储文件，但前半部分包含了一些帮助避免bug的技巧。

将Debug.Assert()放在代码中任何需要进行完整性检查以确保不变量的地方。当编译Release版本时(即没有DEBUG编译器常量)，对DEBUG . assert()的调用将被删除，因此它们不会影响性能。

在调用Debug.Assert()之前仍然应该抛出异常。断言只是确保在开发过程中一切都如预期的那样。

您应该始终使用第二种方法(抛出异常)。

同样，如果你是在生产环境中(并且有一个发布版本)，抛出一个异常(在最坏的情况下让应用程序崩溃)比处理无效值和可能破坏客户数据(这可能要花费数千美元)要好。

我不知道它在c#和。net中是怎样的，但在C中assert()只在使用- ddebug编译时工作-如果没有编译，最终用户将永远不会看到assert()。仅供开发人员使用。我经常使用它，它有时更容易跟踪错误。