Merge pull request #8453 from encukou/rel-error-message

Fix value in error message about negative relative tolerance

Author: kalekundert

src/_pytest/python_api.py

@@ -319,7 +319,7 @@ def set_default(x, default):
 
         if relative_tolerance < 0:
             raise ValueError(
-                f"relative tolerance can't be negative: {absolute_tolerance}"
+                f"relative tolerance can't be negative: {relative_tolerance}"
             )
         if math.isnan(relative_tolerance):
             raise ValueError("relative tolerance can't be NaN.")

testing/python/approx.py

@@ -141,6 +141,13 @@ def test_negative_tolerance(
         with pytest.raises(ValueError):
             1.1 == approx(1, rel, abs)
 
+    def test_negative_tolerance_message(self):
+        # Error message for negative tolerance should include the value.
+        with pytest.raises(ValueError, match="-3"):
+            0 == approx(1, abs=-3)
+        with pytest.raises(ValueError, match="-3"):
+            0 == approx(1, rel=-3)
+
     def test_inf_tolerance(self):
         # Everything should be equal if the tolerance is infinite.
         large_diffs = [(1, 1000), (1e-50, 1e50), (-1.0, -1e300), (0.0, 10)]