add unit tests and refine

Author: aignas

python/private/python.bzl

@@ -250,7 +250,8 @@ def parse_modules(*, module_ctx, _fail = fail):
     other_toolchains = []
     minor_mapping = list(config.minor_mapping.values())
     for t in toolchains:
-        # TODO @aignas 2025-04-04: I am getting lost here when unit testing
+        # FIXME @aignas 2025-04-04: How can we unit test that this ordering is
+        # consistent with what would actually work?
         if config.minor_mapping.get(t.python_version, t.python_version) in minor_mapping:
             minor_version_toolchains.append(t)
         else:

tests/python/python_tests.bzl

@@ -288,16 +288,16 @@ def _test_toolchain_ordering(env):
     py = parse_modules(
         module_ctx = _mock_mctx(
             _mod(
-              name = "my_module", 
-              toolchain = [
-                _toolchain("3.10"),
-                _toolchain("3.10.15"),
-                _toolchain("3.10.16"),
-                _toolchain("3.10.11"),
-                _toolchain("3.11.1"),
-                _toolchain("3.11.10"),
-                _toolchain("3.11.11", is_default = True),
-              ],
+                name = "my_module",
+                toolchain = [
+                    _toolchain("3.10"),
+                    _toolchain("3.10.15"),
+                    _toolchain("3.10.16"),
+                    _toolchain("3.10.11"),
+                    _toolchain("3.11.1"),
+                    _toolchain("3.11.10"),
+                    _toolchain("3.11.11", is_default = True),
+                ],
             ),
             _mod(name = "rules_python", toolchain = [_toolchain("3.11")]),
         ),
@@ -309,25 +309,29 @@ def _test_toolchain_ordering(env):
 
     env.expect.that_str(py.default_python_version).equals("3.11")
     env.expect.that_dict(py.config.minor_mapping).contains_exactly({
-      "3.10": "3.10.16",
-      "3.11": "3.11.11",
-      "3.12": "3.12.9",
-      "3.13": "3.13.2",
-      "3.8": "3.8.20",
-      "3.9": "3.9.21",
+        "3.10": "3.10.16",
+        "3.11": "3.11.11",
+        "3.12": "3.12.9",
+        "3.13": "3.13.2",
+        "3.8": "3.8.20",
+        "3.9": "3.9.21",
     })
     env.expect.that_collection(got_versions).contains_exactly([
-      # First the full-version toolchains that are in minor_mapping
-      # so that they get matched first if only the `python_version` is in MINOR_MAPPING
-      "3.10.16",
-      # Next, the rest, where we will match things based on the `python_version` being
-      # the same
-      "3.10",
-      "3.10.15",
-      "3.10.11",
-      "3.11.1",
-      "3.11.10",
-      "3.11.11",
+        # First the full-version toolchains that are in minor_mapping
+        # so that they get matched first if only the `python_version` is in MINOR_MAPPING
+        #
+        # The default version is always set in the `python_version` flag, so know, that
+        # the default match will be somewhere in the first bunch.
+        "3.10",
+        "3.10.16",
+        "3.11",
+        "3.11.11",
+        # Next, the rest, where we will match things based on the `python_version` being
+        # the same
+        "3.10.15",
+        "3.10.11",
+        "3.11.1",
+        "3.11.10",
     ]).in_order()
 
 _tests.append(_test_toolchain_ordering)