Add description of test variables to contributing guide

CONTRIBUTING.md

@@ -125,8 +125,8 @@ Note that tests will fail automatically if they do not finish execution within 6
 
 #### STDOUT/STDERR and logging capture
 
-When running tests in parallel using `stestr` either via tox, the Makefile (`make
-test_ci`), or in CI, we set the env variable `QISKIT_TEST_CAPTURE_STREAMS`, which will
+When running tests in parallel using `stestr` either via tox
+or in CI, we set the env variable `QISKIT_TEST_CAPTURE_STREAMS`, which will
 capture any text written to stdout, stderr, and log messages and add them as attachments
 to the tests run so output can be associated with the test case it originated from.
 However, if you run tests with `stestr` outside of these mechanisms, by default the
@@ -138,6 +138,18 @@ stdlib unittest runner, a similar result can be accomplished by using the
 [`--buffer`](https://docs.python.org/3/library/unittest.html#command-line-options)
 option (e.g. `python -m unittest discover --buffer ./test/python`).
 
+#### Other testing related settings
+
+The test code defines some environment variables that may occasionally be useful to set:
+
++ `TEST_TIMEOUT`: An integer representing the maximum time a test can take
+  before it is considered a failure.
++ `QE_USE_TESTTOOLS`: Set this variable to `FALSE`, `0`, or `NO` to have the
+  tests use `unittest.TestCase` as the base class. Otherwise, the default is
+`testtools.TestCase` which is an extension of `unittest.TestCase`. In some
+situations, a developer may wish to use a workflow that is not compatible with
+the `testtools` extensions.
+
 ### Code style
 
 The qiskit-experiments repository uses `black` for code formatting and style and

test/base.py

@@ -38,7 +38,7 @@
 # Use testtools by default as a (mostly) drop in replacement for
 # unittest's TestCase. This will enable the fixtures used for capturing stdout
 # stderr, and pylogging to attach the output to stestr's result stream.
-USE_TESTTOOLS = os.environ.get("QE_USE_TESTTOOLS", "TRUE").lower() not in ("false", "0")
+USE_TESTTOOLS = os.environ.get("QE_USE_TESTTOOLS", "TRUE").lower() not in ("false", "0", "no")
 
 
 def create_base_test_case(use_testtools: bool) -> unittest.TestCase: