Add python version checking when using --tox.

test/runner/lib/cli.py

@@ -182,6 +182,10 @@ def parse_args():
                         action='store_true',
                         help='redact sensitive values in output')
 
+    common.add_argument('--check-python',
+                        choices=SUPPORTED_PYTHON_VERSIONS,
+                        help=argparse.SUPPRESS)
+
     test = argparse.ArgumentParser(add_help=False, parents=[common])
 
     test.add_argument('include',

test/runner/lib/config.py

@@ -12,6 +12,7 @@ from lib.util import (
     find_python,
     generate_pip_command,
     get_docker_completion,
+    ApplicationError,
 )
 
 from lib.metadata import (
@@ -67,7 +68,9 @@ class EnvironmentConfig(CommonConfig):
         if self.python == 'default':
             self.python = None
 
-        self.python_version = self.python or '.'.join(str(i) for i in sys.version_info[:2])
+        actual_major_minor = '.'.join(str(i) for i in sys.version_info[:2])
+
+        self.python_version = self.python or actual_major_minor
         self.python_interpreter = args.python_interpreter
 
         self.delegate = self.tox or self.docker or self.remote
@@ -79,6 +82,9 @@ class EnvironmentConfig(CommonConfig):
         self.inject_httptester = args.inject_httptester if 'inject_httptester' in args else False  # type: bool
         self.httptester = docker_qualify_image(args.httptester if 'httptester' in args else '')  # type: str
 
+        if args.check_python and args.check_python != actual_major_minor:
+            raise ApplicationError('Running under Python %s instead of Python %s as expected.' % (actual_major_minor, args.check_python))
+
     @property
     def python_executable(self):
         """

test/runner/lib/delegation.py

@@ -165,6 +165,14 @@ def delegate_tox(args, exclude, require, integration_targets):
         if not args.python:
             cmd += ['--python', version]
 
+        # newer versions of tox do not support older python versions and will silently fall back to a different version
+        # passing this option will allow the delegated ansible-test to verify it is running under the expected python version
+        # tox 3.0.0 dropped official python 2.6 support: https://tox.readthedocs.io/en/latest/changelog.html#v3-0-0-2018-04-02
+        # tox 3.1.3 is the first version to support python 3.8 and later: https://tox.readthedocs.io/en/latest/changelog.html#v3-1-3-2018-08-03
+        # tox 3.1.3 appears to still work with python 2.6, making it a good version to use when supporting all python versions we use
+        # virtualenv 16.0.0 dropped python 2.6 support: https://virtualenv.pypa.io/en/latest/changes/#v16-0-0-2018-05-16
+        cmd += ['--check-python', version]
+
         if isinstance(args, TestConfig):
             if args.coverage and not args.coverage_label:
                 cmd += ['--coverage-label', 'tox-%s' % version]