Which features make a class to be thread-safe?

Question

In MSDN some .NET classes described like this:

\"This type is thread safe.\"

or

\"Public static (Shared in Visual Basic) m

Answer 1

When I use lock(C#) keyword, it means my class is thread-safe or not? When you use lock it means that the portion of code inside the lock {} is thread safe. It doesn't guarantee that your class is thread safe. And as Yochai Timmer said it is not a good idea to lock(this)

How to I evaluate thread-safety of a class? Is there any TESTS to be sure that a class is 100% thread safe? I am not sure there are any tests because it is always possible in multi-threading that you are by chance getting correct results. So in order to be sure you can go through the code of class to see how it is making sure it is thread safe