Explain some testing environment variables

1 files changed, 15 insertions, 0 deletions

diff --git a/doc/contributing.rst b/doc/contributing.rst
index d8317591..71fa6937 100644
--- a/doc/contributing.rst
+++ b/doc/contributing.rst
@@ -128,6 +128,21 @@ To run just a few tests, you can use `pytest test selectors`_::
 These command run the tests in one file, one class, and just one test,
 respectively.
 
+You can also affect the test runs with environment variables:
+
+- COVERAGE_NO_PYTRACER disables the Python tracer if you only want to run the
+  CTracer tests.
+
+- COVERAGE_NO_CTRACER disables the C tracer if you only want to run the
+  PyTracer tests.
+
+- COVEGE_AST_DUMP will dump the AST tree as it is being used during code
+  parsing.
+
+- COVERAGE_KEEP_OUTPUT will save the output files that were generated by the
+  gold-file tests, ones that compare output files to saved gold files.
+
+
 Of course, run all the tests on every version of Python you have, before
 submitting a change.