test: add test for DataFrame._repr_html_ to validate HTML output structure

Author: kosiew

python/tests/test_dataframe.py

@@ -1452,3 +1452,33 @@ def test_dataframe_repr_html(df) -> None:
     body_lines = [f"<td(.*?)>{v}</td>" for inner in body_data for v in inner]
     body_pattern = "(.*?)".join(body_lines)
     assert len(re.findall(body_pattern, output, re.DOTALL)) == 1
+
+
+def test_dataframe_repr_html(df):
+    """Test that DataFrame._repr_html_ produces expected HTML output."""
+    import re
+
+    html = df._repr_html_()
+    assert html is not None
+
+    # Create a more flexible pattern that handles values being wrapped in spans
+    # This pattern will match the sequence of values 1,4,8,2,5,5,3,6,8 regardless of formatting
+    pattern = re.compile(
+        r"<td[^>]*?>(?:<span[^>]*?>)?1(?:</span>)?</td>.*?"
+        + r"<td[^>]*?>(?:<span[^>]*?>)?4(?:</span>)?</td>.*?"
+        + r"<td[^>]*?>(?:<span[^>]*?>)?8(?:</span>)?</td>.*?"
+        + r"<td[^>]*?>(?:<span[^>]*?>)?2(?:</span>)?</td>.*?"
+        + r"<td[^>]*?>(?:<span[^>]*?>)?5(?:</span>)?</td>.*?"
+        + r"<td[^>]*?>(?:<span[^>]*?>)?5(?:</span>)?</td>.*?"
+        + r"<td[^>]*?>(?:<span[^>]*?>)?3(?:</span>)?</td>.*?"
+        + r"<td[^>]*?>(?:<span[^>]*?>)?6(?:</span>)?</td>.*?"
+        + r"<td[^>]*?>(?:<span[^>]*?>)?8(?:</span>)?</td>",
+        re.DOTALL,
+    )
+
+    # Print debug info if the test fails
+    matches = re.findall(pattern, html)
+    if not matches:
+        print(f"HTML output snippet: {html[:500]}...")
+
+    assert len(matches) > 0, "Expected pattern of values not found in HTML output"