test error conditions of client.get_waiter()

tests/test_client.py

@@ -0,0 +1,19 @@
+import pytest
+
+
+@pytest.mark.moto
+def test_get_waiter_not_supported_by_service(sns_client):
+    waiter_name = 'sns_does_not_support_waiters'
+    with pytest.raises(
+        ValueError, match=f'Waiter does not exist: {waiter_name}'
+    ):
+        sns_client.get_waiter(waiter_name)
+
+
+@pytest.mark.moto
+def test_get_waiter_invalid_waiter_name(cloudformation_client):
+    waiter_name = 'this_name_is_invalid'
+    with pytest.raises(
+        ValueError, match=f'Waiter does not exist: {waiter_name}'
+    ):
+        cloudformation_client.get_waiter(waiter_name)