test filters

tests/test_filters.py

@@ -0,0 +1,29 @@
+from rich.color import Color as RichColor
+from rich.color import ColorType
+from rich.segment import Segment
+from rich.style import Style
+from rich.terminal_theme import MONOKAI
+
+from textual.color import Color
+from textual.filter import ANSIToTruecolor
+
+
+def test_ansi_to_truecolor_8_bit_dim():
+    """Test that converting an 8-bit color with dim doesn't crash.
+
+    Regression test for https://github.com/Textualize/textual/issues/5946
+
+    """
+    # Given
+    ansi_filter = ANSIToTruecolor(MONOKAI)
+    test_color = RichColor("color(253)", ColorType.EIGHT_BIT, number=253)
+    test_style = Style(color=test_color, dim=True)
+    segments = [Segment("This should not crash", style=test_style)]
+    background_color = Color(0, 0, 0)
+
+    # When
+    # This line will crash if the bug is present
+    new_segments = ansi_filter.apply(segments, background_color)
+
+    # Then
+    assert new_segments is not None