Fix wildcard mutant patterns selecting no tests for the clean run

src/mutmut/__main__.py

@@ -1090,8 +1090,13 @@ def tests_for_mutant_names(mutant_names: tuple[str, ...] | list[str]) -> set[str
     tests = set()
     for mutant_name in mutant_names:
         if "*" in mutant_name:
+            # Keys are function names (``pkg.mod.x_f``), so a pattern over the mutant
+            # suffix (``pkg.mod.x_f__mutmut_*``) is matched by its function part. This may
+            # select a few extra tests, which is safe for the clean run; selecting none is not,
+            # because an empty selection runs the whole suite.
+            function_pattern = mutant_name.partition("__mutmut_")[0]
             for name, tests_of_this_name in state().tests_by_mangled_function_name.items():
-                if fnmatch.fnmatch(name, mutant_name):
+                if fnmatch.fnmatch(name, function_pattern):
                     tests |= set(tests_of_this_name)
         else:
             tests |= set(state().tests_by_mangled_function_name[mangled_name_from_mutant_name(mutant_name)])

tests/mutation/test_mutation.py

@@ -2055,3 +2055,26 @@ def test_rejects_a_mutant_the_meta_file_does_not_know(self, tmp_path):
             )
 
         assert unknown not in data.exit_code_by_key
+
+
+@pytest.mark.parametrize(
+    "pattern, expected",
+    [
+        # A pattern over the mutant suffix must select the tests of that function only.
+        ("pkg.mod.x_f__mutmut_*", {"test_f"}),
+        ("pkg.mod.x_f__mutmut_1*", {"test_f"}),
+        # Patterns over function names keep working.
+        ("pkg.mod.*", {"test_f", "test_g"}),
+        ("pkg.mod.x_*", {"test_f", "test_g"}),
+    ],
+)
+def test_tests_for_mutant_names_wildcard(pattern, expected):
+    """Regression test for #592: a ``__mutmut_*`` pattern selected no tests, so the clean run fell back to the whole suite."""
+    reset_state()
+    state().tests_by_mangled_function_name["pkg.mod.x_f"] = {"test_f"}
+    state().tests_by_mangled_function_name["pkg.mod.x_g"] = {"test_g"}
+    state().tests_by_mangled_function_name["other.x_h"] = {"test_h"}
+
+    # Called via the module: a bare ``tests_for_*`` import would be collected by pytest as a test.
+    assert mutmut.__main__.tests_for_mutant_names([pattern]) == expected
+    reset_state()