test: change how we keep mismatched actual output

Now when a goldtest has a failure, the actual mismatched output will be written
to the tests/actual directory.

Along the way, I removed some obsolete settings which were only used by unittest
and unittest_mixins, which we no longer use:

- COVERAGE_KEEP_TMP
- COVERAGE_ENV_ID
- $TMPDIR/coverage_test

1 files changed, 0 insertions, 4 deletions

diff --git a/doc/contributing.rst b/doc/contributing.rst
index 09e889c7..1ccb4061 100644
--- a/doc/contributing.rst
+++ b/doc/contributing.rst
@@ -128,10 +128,6 @@ these as 1 to use them:
 - COVERAGE_AST_DUMP: will dump the AST tree as it is being used during code
   parsing.
 
-- COVERAGE_KEEP_TMP: keeps the temporary directories in which tests are run.
-  This makes debugging tests easier. The temporary directories are at
-  ``$TMPDIR/coverage_test/*``, and are named for the test that made them.
-
 
 Of course, run all the tests on every version of Python you have, before
 submitting a change.