launcher: add test for version requirements

Make sure the modules stay in sync in case one is updated but we
forgot to update the other.

Bug: https://crbug.com/gerrit/13795
Change-Id: I6de9533d45c083e5f7ad792ee6d541e23647de3f
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/292444
Reviewed-by: Michael Mortensen <mmortensen@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

tests/test_wrapper.py

@@ -26,6 +26,7 @@ import tempfile
 import unittest
 
 import git_command
+import main
 import platform_utils
 from pyversion import is_python3
 import wrapper
@@ -83,6 +84,16 @@ class RepoWrapperUnitTest(RepoWrapperTestCase):
     self.assertEqual('', stderr.getvalue())
     self.assertIn('repo launcher version', stdout.getvalue())
 
+  def test_python_constraints(self):
+    """The launcher should never require newer than main.py."""
+    self.assertGreaterEqual(main.MIN_PYTHON_VERSION_HARD,
+                            wrapper.MIN_PYTHON_VERSION_HARD)
+    self.assertGreaterEqual(main.MIN_PYTHON_VERSION_SOFT,
+                            wrapper.MIN_PYTHON_VERSION_SOFT)
+    # Make sure the versions are themselves in sync.
+    self.assertGreaterEqual(wrapper.MIN_PYTHON_VERSION_SOFT,
+                            wrapper.MIN_PYTHON_VERSION_HARD)
+
   def test_init_parser(self):
     """Make sure 'init' GetParser works."""
     parser = self.wrapper.GetParser(gitc_init=False)