[libcxx-commits] [libcxx] Update testing documentation with testing guidelines. (PR #87928)

[Christopher Di Bella via libcxx-commits]

================
@@ -180,6 +180,42 @@ The tests of libc++ are stored in libc++'s testing related subdirectories:
   ``libcxx/test/libcxx``. The structure of this directories follows the
   structure of ``libcxx/test/std``.
 
+Principles of testing
+---------------------
+
+Tests are a practical way to validate the correctness of the code. As such, they contain pragmatic trade offs between
+the cost of writing and maintaining the tests and the value they provide. Please consider the following principles when
+writing tests:
+
+- **Consider the next reader**
----------------
cjdb wrote:

Do we want people to "consider X" when writing tests, or do we want them to take bold action instead?

As an example, perhaps "tests should be resilient to change over time" gets the developer to consider the effect of time, but also gives something actionable in the title (which is probably what will be remembered).

https://github.com/llvm/llvm-project/pull/87928