bpo-45629: Add a test for the "freeze" tool. (gh-29222)

The "freeze" tool has been part of the repo for a long time. However, it hasn't had any tests in the test suite to guard against regressions. We add such a test here. This is especially important as there has been a lot of change recently related to frozen modules, with more to come.

Note that as part of the test we build Python out-of-tree and install it in a temp dir.

https://bugs.python.org/issue45629

Lib/test/test_tools/test_freeze.py

@@ -0,0 +1,29 @@
+"""Sanity-check tests for the "freeze" tool."""
+
+import sys
+import textwrap
+import unittest
+
+from test import support
+
+from . import imports_under_tool, skip_if_missing
+skip_if_missing('freeze')
+with imports_under_tool('freeze', 'test'):
+    import freeze as helper
+
+
+@unittest.skipIf(sys.platform.startswith('win'), 'not supported on Windows')
+@support.skip_if_buildbot('not all buildbots have enough space')
+class TestFreeze(unittest.TestCase):
+
+    def test_freeze_simple_script(self):
+        script = textwrap.dedent("""
+            import sys
+            print('running...')
+            sys.exit(0)
+            """)
+        outdir, scriptfile, python = helper.prepare(script)
+
+        executable = helper.freeze(python, scriptfile, outdir)
+        text = helper.run(executable)
+        self.assertEqual(text, 'running...')