gh-128613: Increase typing.Concatenate coverage (#128614)

Author: sobolevn

Lib/test/test_typing.py

@@ -10129,6 +10129,18 @@ def test_valid_uses(self):
         self.assertEqual(C4.__args__, (Concatenate[int, T, P], T))
         self.assertEqual(C4.__parameters__, (T, P))
 
+    def test_invalid_uses(self):
+        with self.assertRaisesRegex(TypeError, 'Concatenate of no types'):
+            Concatenate[()]
+        with self.assertRaisesRegex(
+            TypeError,
+            (
+                'The last parameter to Concatenate should be a '
+                'ParamSpec variable or ellipsis'
+            ),
+        ):
+            Concatenate[int]
+
     def test_var_substitution(self):
         T = TypeVar('T')
         P = ParamSpec('P')