test invalid cmap name

Co-authored-by: @neutrinoceros

Author: DanielYang59

cmasher/tests/test_utils.py

@@ -116,6 +116,14 @@ def test_not_enough_cmaps(self, cmaps):
         ):
             combine_cmaps(cmaps)
 
+    # Test if invalid colormap name raise an error
+    def test_invalid_cmap_name(self):
+        with pytest.raises(
+            KeyError,
+            match="'fake_cmap' is not a known colormap name",
+        ):
+            combine_cmaps(cmaps=["fake_cmap", "Blues"])
+
     # Test if invalid colormap types raise an error
     @pytest.mark.parametrize(
         "invalid_cmap",