add test showing bug

Author: archmoj

test/image/baselines/zz-heatmap-text-color-on-missing-data.png

@@ -0,0 +1,60 @@
+{
+    "data": [
+        {
+            "colorscale": "Reds",
+            "text": [
+                [
+                    "One",
+                    "Two",
+                    "Three"
+                ],
+                [
+                    "Four",
+                    "Five",
+                    "Six"
+                ],
+                [
+                    "Seven",
+                    "Eight",
+                    "Nine"
+                ]
+            ],
+            "texttemplate": "%{text}",
+            "x": [
+                0,
+                1,
+                2
+            ],
+            "y": [
+                0,
+                1,
+                2
+            ],
+            "z": [
+                [
+                    null,
+                    2,
+                    3
+                ],
+                [
+                    4,
+                    null,
+                    6
+                ],
+                [
+                    7,
+                    8,
+                    null
+                ]
+            ],
+            "type": "heatmap"
+        }
+    ],
+    "layout": {
+        "title": {
+            "text": "Heatmap text color should contrast with<br>background on cells with missing data"
+        },
+        "width": 400,
+        "height": 400
+    }
+}