tests(textframe): Add pytest_assertrepr_compare hook

why: Provide rich assertion output for TextFrame comparisons
without requiring syrupy for basic equality checks.
what:
- Add pytest_assertrepr_compare hook for TextFrame == TextFrame
- Show dimension mismatches (width, height)
- Show content diff using difflib.ndiff

Author: tony

tests/textframe/conftest.py

@@ -2,12 +2,67 @@
 
 from __future__ import annotations
 
+import typing as t
+from difflib import ndiff
+
 import pytest
 from syrupy.assertion import SnapshotAssertion
 
+from .core import TextFrame
 from .plugin import TextFrameExtension
 
 
+def pytest_assertrepr_compare(
+    config: pytest.Config,
+    op: str,
+    left: t.Any,
+    right: t.Any,
+) -> list[str] | None:
+    """Provide rich assertion output for TextFrame comparisons.
+
+    This hook provides detailed diff output when two TextFrame objects
+    are compared with ==, showing dimension mismatches and content diffs.
+
+    Parameters
+    ----------
+    config : pytest.Config
+        The pytest configuration object.
+    op : str
+        The comparison operator (e.g., "==", "!=").
+    left : Any
+        The left operand of the comparison.
+    right : Any
+        The right operand of the comparison.
+
+    Returns
+    -------
+    list[str] | None
+        List of explanation lines, or None to use default behavior.
+    """
+    if not isinstance(left, TextFrame) or not isinstance(right, TextFrame):
+        return None
+    if op != "==":
+        return None
+
+    lines = ["TextFrame comparison failed:"]
+
+    # Dimension mismatch
+    if left.content_width != right.content_width:
+        lines.append(f"  width: {left.content_width} != {right.content_width}")
+    if left.content_height != right.content_height:
+        lines.append(f"  height: {left.content_height} != {right.content_height}")
+
+    # Content diff
+    left_render = left.render().splitlines()
+    right_render = right.render().splitlines()
+    if left_render != right_render:
+        lines.append("")
+        lines.append("Content diff:")
+        lines.extend(ndiff(right_render, left_render))
+
+    return lines
+
+
 @pytest.fixture
 def snapshot(snapshot: SnapshotAssertion) -> SnapshotAssertion:
     """Override default snapshot fixture to use TextFrameExtension.