fixup! [libcxx][docs] Make test name pattern documentation more obvious

Add recommendation on when to write verify tests.

Author: hawkinsw

libcxx/docs/TestingLibcxx.rst

@@ -351,15 +351,23 @@ Test Filenames`_ when determining the names for new test files.
      - Same as ``FOO.pass.cpp``, but for Objective-C++.
 
    * - ``FOO.compile.pass.cpp``
-     - Checks whether the C++ code in the file compiles successfully.
+     - Checks whether the C++ code in the file compiles successfully. In general, prefer `compile` tests over `verify` tests, 
+       subject to the specific recommendations, below, for when to write `verify` tests.
    * - ``FOO.compile.pass.mm``
      - Same as ``FOO.compile.pass.cpp``, but for Objective-C++.
    * - ``FOO.compile.fail.cpp``
      - Checks that the code in the file does *not* compile successfully.
 
    * - ``FOO.verify.cpp``
      - Compiles with clang-verify. This type of test is automatically marked as UNSUPPORTED if the compiler does not support clang-verify.
-       For additional information about how to write tests using ``clang-verify``, see the `Internals Manual <https://clang.llvm.org/docs/InternalsManual.html#verifying-diagnostics>`_.
+       For additional information about how to write `verify` tests, see the `Internals Manual <https://clang.llvm.org/docs/InternalsManual.html#verifying-diagnostics>`_.
+       Prefer `verify` tests over `compile` tests to test that compilation fails for a particular reason. For example, use a `verify` test
+       to ensure that
+
+       * an expected ``static_assert`` is triggered;
+       * the use of deprecated functions generates the proper warning;
+       * removed functions are no longer usable; or
+       * return values from functions marked ``[[nodiscard]]`` are stored.
 
    * - ``FOO.link.pass.cpp``
      - Checks that the C++ code in the file compiles and links successfully -- no run attempted.