extend cmaps length test

Co-authored-by: @neutrinoceros

Author: DanielYang59

cmasher/tests/test_utils.py

@@ -97,10 +97,24 @@ def test_combine_cmaps(self, cmaps, nodes):
 
         assert combined_cmap.N == 256
 
-    # Test if combining a single colormap raises an error
-    def test_single_cmap(self):
-        with pytest.raises(ValueError, match="Cannot combine a single colormap."):
-            combine_cmaps(cmaps=["Blues"])
+    # Test if combining less than 2 colormaps triggers an error
+    @pytest.mark.parametrize(
+        "cmaps",
+        [
+            pytest.param([], id="no_cmap"),
+            pytest.param(
+                [
+                    "Blues",
+                ],
+                id="single_cmap",
+            ),
+        ],
+    )
+    def test_single_cmap(self, cmaps):
+        with pytest.raises(
+            ValueError, match="Expected at least two colormaps to combine."
+        ):
+            combine_cmaps(cmaps)
 
     # Test if invalid colormap types raise an error
     @pytest.mark.parametrize(
@@ -115,7 +129,12 @@ def test_invalid_cmap_types(self, invalid_cmap):
             combine_cmaps(cmaps=["Blues", invalid_cmap])
 
     # Test if invalid nodes types raise an error
-    @pytest.mark.parametrize("invalid_nodes", [0.5,],)
+    @pytest.mark.parametrize(
+        "invalid_nodes",
+        [
+            0.5,
+        ],
+    )
     def test_invalid_nodes_types(self, invalid_nodes):
         with pytest.raises(
             TypeError,

cmasher/utils.py

@@ -296,8 +296,8 @@ def combine_cmaps(
 
     """
     # Check colormap datatype and convert to list[Colormap]
-    if len(cmaps) == 1:
-        raise ValueError("Cannot combine a single colormap.")
+    if len(cmaps) <= 1:
+        raise ValueError("Expected at least two colormaps to combine.")
     for cm in cmaps:
         if not isinstance(cm, (Colormap, str)):
             raise TypeError(f"Unsupported colormap type: {type(cm)}.")