add a "fast" environment in tox to exit as soon as any test fails

The default in CI is still to run all of the tests.

Author: dhellmann

docs/source/developers.rst

@@ -86,6 +86,11 @@ Python::
 
   $ tox -e py27 tests/test_cd.sh
 
+To stop the test suite as soon as any test fails, use the `fast` tox
+target::
+
+  $ tox -e fast
+
 Add new tests by modifying an existing file or creating new script in
 the ``tests`` directory.
 

tests/run_tests

@@ -14,6 +14,9 @@ then
     fi
 fi
 
+# Override FAIL_FAST to true to exit as soon as any test fails
+FAIL_FAST=${FAIL_FAST:-false}
+
 # Force the tox virtualenv to be active.
 #
 # Since this script runs from within a separate shell created by tox,
@@ -69,6 +72,9 @@ do
     export SHUNIT_PARENT
     if ! $SHELL $test_shell_opts $test_script; then
         RC=1
+        if $FAIL_FAST; then
+            exit $RC
+        fi
     fi
     echo
 

tox.ini

@@ -13,6 +13,12 @@ allowlist_externals =
     zsh
     ksh
 
+[testenv:fast]
+setenv =
+    TOXIC = true
+    SHELL = /bin/bash
+    FAIL_FAST = true
+
 [testenv:style]
 deps = flake8
 commands = flake8 virtualenvwrapper docs/source/conf.py