test: fix Python unittests in ./test and ./tools

Co-authored-by: @patrickhousley

Fixes to Python tests to ensure that the following all pass:
1. __python2 -m pytest ./test ./tools__  # 30 tests pass
2. __python3 -m pytest ./test ./tools__  # 30 tests pass
3. __python2 -m unittest discover -s ./test/tools__  # 1 test passes
4. __python3 -m unittest discover -s ./test/tools__  # 1 test passes
5. __PYTHON=python2 make tooltest__   # 1 test passes
6. __PYTHON=python3 make tooltest__   # 1 test passes

This is a subset of #30033

Makefile

@@ -300,7 +300,7 @@ jstest: build-addons build-js-native-api-tests build-node-api-tests ## Runs addo
 
 .PHONY: tooltest
 tooltest:
-	@$(PYTHON) test/tools/test-js2c.py
+	@$(PYTHON) -m unittest discover -s ./test/tools
 
 .PHONY: coverage-run-js
 coverage-run-js:

tools/gyp/pylib/gyp/MSVSSettings_test.py

@@ -6,15 +6,19 @@
 
 """Unit tests for the MSVSSettings.py file."""
 
-import StringIO
 import unittest
 import gyp.MSVSSettings as MSVSSettings
 
+try:
+  from StringIO import StringIO  # Python 2
+except ImportError:
+  from io import StringIO  # Python 3
+
 
 class TestSequenceFunctions(unittest.TestCase):
 
   def setUp(self):
-    self.stderr = StringIO.StringIO()
+    self.stderr = StringIO()
 
   def _ExpectedWarnings(self, expected):
     """Compares recorded lines to expected warnings."""

tools/gyp/pylib/gyp/common.py

@@ -2,14 +2,18 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-import collections
 import errno
 import filecmp
 import os.path
 import re
 import tempfile
 import sys
 
+try:
+  from collections.abc import MutableSet
+except ImportError:
+  from collections import MutableSet
+
 
 # A minimal memoizing decorator. It'll blow up if the args aren't immutable,
 # among other "problems".
@@ -493,7 +497,7 @@ def uniquer(seq, idfun=None):
 
 
 # Based on http://code.activestate.com/recipes/576694/.
-class OrderedSet(collections.MutableSet):
+class OrderedSet(MutableSet):
   def __init__(self, iterable=None):
     self.end = end = []
     end += [None, end, end]         # sentinel node for doubly linked list

tools/gyp/pylib/gyp/easy_xml_test.py

@@ -8,13 +8,17 @@
 
 import gyp.easy_xml as easy_xml
 import unittest
-import StringIO
+
+try:
+  from StringIO import StringIO  # Python 2
+except ImportError:
+  from io import StringIO  # Python 3
 
 
 class TestSequenceFunctions(unittest.TestCase):
 
   def setUp(self):
-    self.stderr = StringIO.StringIO()
+    self.stderr = StringIO()
 
   def test_EasyXml_simple(self):
     self.assertEqual(

tools/gyp/pylib/gyp/generator/msvs_test.py

@@ -7,13 +7,17 @@
 
 import gyp.generator.msvs as msvs
 import unittest
-import StringIO
+
+try:
+  from StringIO import StringIO  # Python 2
+except ImportError:
+  from io import StringIO  # Python 3
 
 
 class TestSequenceFunctions(unittest.TestCase):
 
   def setUp(self):
-    self.stderr = StringIO.StringIO()
+    self.stderr = StringIO()
 
   def test_GetLibraries(self):
     self.assertEqual(

tools/gyp/pylib/gyp/generator/ninja_test.py

@@ -6,11 +6,10 @@
 
 """ Unit tests for the ninja.py file. """
 
-import gyp.generator.ninja as ninja
-import unittest
-import StringIO
 import sys
-import TestCommon
+import unittest
+
+import gyp.generator.ninja as ninja
 
 
 class TestPrefixesAndSuffixes(unittest.TestCase):