diff --git a/Lib/test/test_script_helper.py b/Lib/test/test_script_helper.py
new file mode 100644
index 000000000..4ade2cbc0
--- /dev/null
+++ b/Lib/test/test_script_helper.py
@@ -0,0 +1,125 @@
+"""Unittests for test.support.script_helper.  Who tests the test helper?"""
+
+import subprocess
+import sys
+import os
+from test.support import script_helper
+import unittest
+from unittest import mock
+
+
+class TestScriptHelper(unittest.TestCase):
+
+    def test_assert_python_ok(self):
+        t = script_helper.assert_python_ok('-c', 'import sys; sys.exit(0)')
+        self.assertEqual(0, t[0], 'return code was not 0')
+
+    def test_assert_python_failure(self):
+        # I didn't import the sys module so this child will fail.
+        rc, out, err = script_helper.assert_python_failure('-c', 'sys.exit(0)')
+        self.assertNotEqual(0, rc, 'return code should not be 0')
+
+    def test_assert_python_ok_raises(self):
+        # I didn't import the sys module so this child will fail.
+        with self.assertRaises(AssertionError) as error_context:
+            script_helper.assert_python_ok('-c', 'sys.exit(0)')
+        error_msg = str(error_context.exception)
+        self.assertIn('command line:', error_msg)
+        self.assertIn('sys.exit(0)', error_msg, msg='unexpected command line')
+
+    def test_assert_python_failure_raises(self):
+        with self.assertRaises(AssertionError) as error_context:
+            script_helper.assert_python_failure('-c', 'import sys; sys.exit(0)')
+        error_msg = str(error_context.exception)
+        self.assertIn('Process return code is 0\n', error_msg)
+        self.assertIn('import sys; sys.exit(0)', error_msg,
+                      msg='unexpected command line.')
+
+    @mock.patch('subprocess.Popen')
+    def test_assert_python_isolated_when_env_not_required(self, mock_popen):
+        with mock.patch.object(script_helper,
+                               'interpreter_requires_environment',
+                               return_value=False) as mock_ire_func:
+            mock_popen.side_effect = RuntimeError('bail out of unittest')
+            try:
+                script_helper._assert_python(True, '-c', 'None')
+            except RuntimeError as err:
+                self.assertEqual('bail out of unittest', err.args[0])
+            self.assertEqual(1, mock_popen.call_count)
+            self.assertEqual(1, mock_ire_func.call_count)
+            popen_command = mock_popen.call_args[0][0]
+            self.assertEqual(sys.executable, popen_command[0])
+            self.assertIn('None', popen_command)
+            self.assertIn('-I', popen_command)
+            self.assertNotIn('-E', popen_command)  # -I overrides this
+
+    @mock.patch('subprocess.Popen')
+    def test_assert_python_not_isolated_when_env_is_required(self, mock_popen):
+        """Ensure that -I is not passed when the environment is required."""
+        with mock.patch.object(script_helper,
+                               'interpreter_requires_environment',
+                               return_value=True) as mock_ire_func:
+            mock_popen.side_effect = RuntimeError('bail out of unittest')
+            try:
+                script_helper._assert_python(True, '-c', 'None')
+            except RuntimeError as err:
+                self.assertEqual('bail out of unittest', err.args[0])
+            popen_command = mock_popen.call_args[0][0]
+            self.assertNotIn('-I', popen_command)
+            self.assertNotIn('-E', popen_command)
+
+
+class TestScriptHelperEnvironment(unittest.TestCase):
+    """Code coverage for interpreter_requires_environment()."""
+
+    def setUp(self):
+        self.assertTrue(
+            hasattr(script_helper, '__cached_interp_requires_environment'))
+        # Reset the private cached state.
+        script_helper.__dict__['__cached_interp_requires_environment'] = None
+
+    def tearDown(self):
+        # Reset the private cached state.
+        script_helper.__dict__['__cached_interp_requires_environment'] = None
+
+    @mock.patch('subprocess.check_call')
+    def test_interpreter_requires_environment_true(self, mock_check_call):
+        with mock.patch.dict(os.environ):
+            os.environ.pop('PYTHONHOME', None)
+            mock_check_call.side_effect = subprocess.CalledProcessError('', '')
+            self.assertTrue(script_helper.interpreter_requires_environment())
+            self.assertTrue(script_helper.interpreter_requires_environment())
+            self.assertEqual(1, mock_check_call.call_count)
+
+    @mock.patch('subprocess.check_call')
+    def test_interpreter_requires_environment_false(self, mock_check_call):
+        with mock.patch.dict(os.environ):
+            os.environ.pop('PYTHONHOME', None)
+            # The mocked subprocess.check_call fakes a no-error process.
+            script_helper.interpreter_requires_environment()
+            self.assertFalse(script_helper.interpreter_requires_environment())
+            self.assertEqual(1, mock_check_call.call_count)
+
+    @mock.patch('subprocess.check_call')
+    def test_interpreter_requires_environment_details(self, mock_check_call):
+        with mock.patch.dict(os.environ):
+            os.environ.pop('PYTHONHOME', None)
+            script_helper.interpreter_requires_environment()
+            self.assertFalse(script_helper.interpreter_requires_environment())
+            self.assertFalse(script_helper.interpreter_requires_environment())
+            self.assertEqual(1, mock_check_call.call_count)
+            check_call_command = mock_check_call.call_args[0][0]
+            self.assertEqual(sys.executable, check_call_command[0])
+            self.assertIn('-E', check_call_command)
+
+    @mock.patch('subprocess.check_call')
+    def test_interpreter_requires_environment_with_pythonhome(self, mock_check_call):
+        with mock.patch.dict(os.environ):
+            os.environ['PYTHONHOME'] = 'MockedHome'
+            self.assertTrue(script_helper.interpreter_requires_environment())
+            self.assertTrue(script_helper.interpreter_requires_environment())
+            self.assertEqual(0, mock_check_call.call_count)
+
+
+if __name__ == '__main__':
+    unittest.main()