fix zero division error (#2674)

* fix zero division error

* push tests

tests/test_resolve.py

@@ -5,6 +5,7 @@ import pytest
 
 from textual._resolve import resolve, resolve_fraction_unit
 from textual.css.scalar import Scalar
+from textual.css.styles import Styles
 from textual.geometry import Size
 from textual.widget import Widget
 
@@ -125,6 +126,30 @@ def test_resolve_fraction_unit():
     ) == Fraction(2)
 
 
+def test_resolve_fraction_unit_stress_test():
+    """Check for zero division errors."""
+    # https://github.com/Textualize/textual/issues/2673
+    widget = Widget()
+    styles = widget.styles
+    styles.width = "1fr"
+
+    # We're mainly checking for the absence of zero division errors,
+    # which is a reoccurring theme for this code.
+    for remaining_space in range(1, 101, 10):
+        for max_width in range(1, remaining_space):
+            styles.max_width = max_width
+
+            for width in range(1, remaining_space):
+                resolved_unit = resolve_fraction_unit(
+                    [styles, styles, styles],
+                    Size(width, 24),
+                    Size(width, 24),
+                    Fraction(remaining_space),
+                    "width",
+                )
+                assert resolved_unit <= remaining_space
+
+
 def test_resolve_issue_2502():
     """Test https://github.com/Textualize/textual/issues/2502"""