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

[Christopher Di Bella via libcxx-commits]

================
@@ -180,6 +180,38 @@ 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**
+
+    Tests should be obvious to the future reader. Avoid too much boiler plate or other
+    distractions. Ensure each test has enough context to understand what it is testing. Avoid gratuitous use of advanced
+    test features or abstractions.
+
+- **Consider the effect of time**
----------------
cjdb wrote:

Consider rephrasing the title. I thought "time" meant "build time" or "run-time", not "things change over time".

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