bpo-32942: Fix environment dependent test_script_helper (GH-8034)

Result of function interpreter_requires_environment() depends on os.environ.
This was not covered by the tests, leading to fail when PYTHONHOME was set.

Lib/test/test_script_helper.py

@@ -2,6 +2,7 @@
 
 import subprocess
 import sys
+import os
 from test.support import script_helper
 import unittest
 from unittest import mock
@@ -73,7 +74,7 @@ class TestScriptHelperEnvironment(unittest.TestCase):
 
     def setUp(self):
         self.assertTrue(
-                hasattr(script_helper, '__cached_interp_requires_environment'))
+            hasattr(script_helper, '__cached_interp_requires_environment'))
         # Reset the private cached state.
         script_helper.__dict__['__cached_interp_requires_environment'] = None
 
@@ -83,27 +84,41 @@ class TestScriptHelperEnvironment(unittest.TestCase):
 
     @mock.patch('subprocess.check_call')
     def test_interpreter_requires_environment_true(self, mock_check_call):
-        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)
+        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):
-        # 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)
+        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):
-        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)
+        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__':