test: add custom cell builder test for HTML formatter with value-based styling

Author: kosiew

python/tests/test_dataframe.py

@@ -733,6 +733,83 @@ def format_int(value):
 def test_html_formatter_custom_cell_builder(df, clean_formatter_state):
     """Test using a custom cell builder function."""
 
+    def test_html_formatter_custom_cell_builder(df, clean_formatter_state):
+        """Test using a custom cell builder function that changes style based on value."""
+
+        # Create a custom cell builder with distinct styling for different value ranges
+        def custom_cell_builder(value, row, col, table_id):
+            try:
+                num_value = int(value)
+                if num_value > 5:  # Values > 5 get green background with indicator
+                    return f'<td style="background-color: #d9f0d3" data-test="high">{value}-high</td>'
+                if num_value < 3:  # Values < 3 get blue background with indicator
+                    return f'<td style="background-color: #d3e9f0" data-test="low">{value}-low</td>'
+            except (ValueError, TypeError):
+                pass
+
+            # Default styling for other cells (3, 4, 5)
+            return (
+                f'<td style="border: 1px solid #ddd" data-test="mid">{value}-mid</td>'
+            )
+
+        # Set our custom cell builder
+        formatter = get_formatter()
+        formatter.set_custom_cell_builder(custom_cell_builder)
+
+        html_output = df._repr_html_()
+
+        # Extract cells with specific styling using regex
+        low_cells = re.findall(
+            r'<td style="background-color: #d3e9f0"[^>]*>(\d+)-low</td>', html_output
+        )
+        mid_cells = re.findall(
+            r'<td style="border: 1px solid #ddd"[^>]*>(\d+)-mid</td>', html_output
+        )
+        high_cells = re.findall(
+            r'<td style="background-color: #d9f0d3"[^>]*>(\d+)-high</td>', html_output
+        )
+
+        # Sort the extracted values for consistent comparison
+        low_cells = sorted(map(int, low_cells))
+        mid_cells = sorted(map(int, mid_cells))
+        high_cells = sorted(map(int, high_cells))
+
+        # Verify specific values have the correct styling applied
+        assert low_cells == [1, 2]  # Values < 3
+        assert mid_cells == [3, 4, 5, 5]  # Values 3-5
+        assert high_cells == [6, 8, 8]  # Values > 5
+
+        # Verify the exact content with styling appears in the output
+        assert (
+            '<td style="background-color: #d3e9f0" data-test="low">1-low</td>'
+            in html_output
+        )
+        assert (
+            '<td style="background-color: #d3e9f0" data-test="low">2-low</td>'
+            in html_output
+        )
+        assert (
+            '<td style="border: 1px solid #ddd" data-test="mid">3-mid</td>'
+            in html_output
+        )
+        assert (
+            '<td style="border: 1px solid #ddd" data-test="mid">4-mid</td>'
+            in html_output
+        )
+        assert (
+            '<td style="background-color: #d9f0d3" data-test="high">6-high</td>'
+            in html_output
+        )
+        assert (
+            '<td style="background-color: #d9f0d3" data-test="high">8-high</td>'
+            in html_output
+        )
+
+        # Count occurrences to ensure all cells are properly styled
+        assert html_output.count("-low</td>") == 2  # Two low values (1, 2)
+        assert html_output.count("-mid</td>") == 4  # Four mid values (3, 4, 5, 5)
+        assert html_output.count("-high</td>") == 3  # Three high values (6, 8, 8)
+
     # Create a custom cell builder that changes background color based on value
     def custom_cell_builder(value, row, col, table_id):
         # Handle numeric values regardless of their exact type