gh-106368: Argument Clinic: Test that keyword params are disallowed i…

…n groups (#107985)

Lib/test/test_clinic.py

@@ -1524,6 +1524,27 @@ def test_disallowed_grouping__no_matching_bracket(self):
         err = "Function 'empty_group' has a ']' without a matching '['"
         self.expect_failure(block, err)
 
+    def test_disallowed_grouping__must_be_position_only(self):
+        dataset = ("""
+            with_kwds
+                [
+                *
+                a: object
+                ]
+        """, """
+            with_kwds
+                [
+                a: object
+                ]
+        """)
+        err = (
+            "You cannot use optional groups ('[' and ']') unless all "
+            "parameters are positional-only ('/')"
+        )
+        for block in dataset:
+            with self.subTest(block=block):
+                self.expect_failure(block, err)
+
     def test_no_parameters(self):
         function = self.parse_function("""
             module foo