Update test-suite docs. NFC (#25774)

Author: sbc100

site/source/docs/getting_started/test-suite.rst

@@ -204,9 +204,20 @@ To further customize how the benchmarks are run, you will want to edit the file
 Debugging test failures
 =======================
 
-Setting the :ref:`debugging-EMCC_DEBUG` is useful for debugging tests, as it
-emits debug output and intermediate files (the files go in
-**/tmp/emscripten_temp/**):
+By default the test runner will hide all test output and use a single terminal
+line to show test results.
+
+If you want to see more information you can run with ``-v/--verbose`` to show the
+stdout / stderr / logging produced during each test.
+
+If you add a second ``-v/--verbose`` then then test runner will output even more
+information.  For example it will show all the subcommands that it runs, as it
+runs them.
+
+For even more debugging info, you can set :ref:`debugging-EMCC_DEBUG` which will
+cause the emscripten compiler itself to output a lot of debug info.  This will
+also tell the compiler to leave all its temporary files behind after it runs 
+(the files go in ``/tmp/emscripten_temp/``):
 
 .. code-block:: bash
 
@@ -222,11 +233,11 @@ emits debug output and intermediate files (the files go in
   EMCC_DEBUG=2 test/runner test_hello_world
 
 
-You can also specify ``--save-dir`` to save the temporary directory that the
-test runner uses into **/out/test/**.  This is a test suite-specific
-feature, and is useful for inspecting test outputs as well as temporary files
-generated by the test.  By default, the temporary directory will be cleaned
-between each test run, but you can add ``--no-clean`` to avoid this.
+If you run just one a single test (or one test at at time using ``-j1``) the test
+output can always be found in ``out/test``.  This is useful for inspecting test
+outputs as well as temporary files generated by the test.  By default, the temporary
+directory will be cleaned between each test run, but you can add ``--no-clean`` to
+avoid this.
 
 The :ref:`Debugging` topic provides more guidance on how to debug
 Emscripten-generated code.