comment on test suite debugging

1 files changed, 10 insertions, 0 deletions

diff --git a/tests/runner.py b/tests/runner.py
index 69ce8107..501299c7 100755
--- a/tests/runner.py
+++ b/tests/runner.py
@@ -798,6 +798,16 @@ an individual test with
 
   python tests/runner.py ALL.test_hello_world
 
+Debugging: You can run
+
+  EM_SAVE_DIR=1 python tests/runner.py ALL.test_hello_world
+
+in order to save the test runner directory, in /tmp/emscripten_temp. All files
+created by the test will be present there. You can also use EMCC_DEBUG to
+further debug the compiler itself, which works outside of the test suite as
+well: EMCC_DEBUG=1 will emit emcc-* files in that temp dir for each stage
+of the compiler, while EMCC_DEBUG=2 will emit even more files, one for each
+js optimizer phase.
 ==============================================================================
 
 '''