recwarn: improved warns(match=...) error message on regex mismatch (closes pytest-dev#11225) (pytest-dev#14310)

When using pytest.warns(match=...), even if a warning of the expected type was emitted, the first sentence of the error message said "DID NOT WARN" when the regex did not match. Since this made it seem as though no warning had been emitted at all, I updated it to make the situation clearer.

Closes pytest-dev#11225

Author: JaeHyuckSa

AUTHORS

@@ -209,6 +209,7 @@ Israël Hallé
 Itxaso Aizpurua
 Iwan Briquemont
 Jaap Broekhuizen
+JaeHyuck Sa
 Jake VanderPlas
 Jakob van Santen
 Jakub Mitoraj

changelog/11225.improvement.rst

@@ -0,0 +1 @@
+:func:`pytest.warns` now shows "Regex pattern did not match" instead of "DID NOT WARN" when warnings were emitted but the ``match`` pattern did not match.

doc/en/how-to/capture-warnings.rst

@@ -363,7 +363,9 @@ Some examples:
     ...
     Traceback (most recent call last):
       ...
-    Failed: DID NOT WARN. No warnings of type ...UserWarning... were emitted...
+    Failed: Regex pattern did not match any of the 1 warnings emitted.
+     Regex: ...
+     Emitted warnings: ...UserWarning...
 
     >>> with warns(UserWarning, match=re.escape("issue with foo() func")):
     ...     warnings.warn("issue with foo() func")

src/_pytest/recwarn.py

@@ -139,7 +139,9 @@ def warns(
         ...         warnings.warn("this is not here", UserWarning)
         Traceback (most recent call last):
           ...
-        Failed: DID NOT WARN. No warnings of type ...UserWarning... were emitted...
+        Failed: Regex pattern did not match any of the 1 warnings emitted.
+         Regex: ...
+         Emitted warnings: ...UserWarning...
 
     **Using with** ``pytest.mark.parametrize``
 
@@ -321,10 +323,17 @@ def found_str() -> str:
                     f" Emitted warnings: {found_str()}."
                 )
             elif not any(self.matches(w) for w in self):
+                escape_hint = ""
+                if isinstance(self.match_expr, str) and any(
+                    self.match_expr == str(w.message)
+                    for w in self
+                    if issubclass(w.category, self.expected_warning)
+                ):
+                    escape_hint = "\n Did you mean to `re.escape()` the regex?"
                 fail(
-                    f"DID NOT WARN. No warnings of type {self.expected_warning} matching the regex were emitted.\n"
-                    f" Regex: {self.match_expr}\n"
-                    f" Emitted warnings: {found_str()}."
+                    f"Regex pattern did not match any of the {len(self)} warnings emitted.\n"
+                    f" Regex: {self.match_expr!r}\n"
+                    f" Emitted warnings: {found_str()}.{escape_hint}"
                 )
         finally:
             # Whether or not any warnings matched, we want to re-emit all unmatched warnings.

testing/test_recwarn.py

@@ -243,7 +243,9 @@ def test_deprecated_call_supports_match(self) -> None:
             warnings.warn("value must be 42", DeprecationWarning)
 
         with pytest.deprecated_call():
-            with pytest.raises(pytest.fail.Exception, match="DID NOT WARN"):
+            with pytest.raises(
+                pytest.fail.Exception, match="Regex pattern did not match"
+            ):
                 with pytest.deprecated_call(match=r"must be \d+$"):
                     warnings.warn("this is not here", DeprecationWarning)
 
@@ -406,7 +408,9 @@ def test_match_regex(self) -> None:
 
     def test_one_from_multiple_warns(self) -> None:
         with pytest.warns():
-            with pytest.raises(pytest.fail.Exception, match="DID NOT WARN"):
+            with pytest.raises(
+                pytest.fail.Exception, match="Regex pattern did not match"
+            ):
                 with pytest.warns(UserWarning, match=r"aaa"):
                     with pytest.warns(UserWarning, match=r"aaa"):
                         warnings.warn("cccccccccc", UserWarning)
@@ -415,11 +419,38 @@ def test_one_from_multiple_warns(self) -> None:
 
     def test_none_of_multiple_warns(self) -> None:
         with pytest.warns():
-            with pytest.raises(pytest.fail.Exception, match="DID NOT WARN"):
+            with pytest.raises(
+                pytest.fail.Exception, match="Regex pattern did not match"
+            ):
                 with pytest.warns(UserWarning, match=r"aaa"):
                     warnings.warn("bbbbbbbbbb", UserWarning)
                     warnings.warn("cccccccccc", UserWarning)
 
+    def test_warns_match_failure_message_detail(self) -> None:
+        with pytest.warns():
+            with pytest.raises(pytest.fail.Exception) as excinfo:
+                with pytest.warns(UserWarning, match=r"must be \d+$"):
+                    warnings.warn("this is not here", UserWarning)
+        msg = str(excinfo.value)
+        assert "Regex pattern did not match" in msg
+        assert "this is not here" in msg
+        assert "DID NOT WARN" not in msg
+
+    def test_warns_match_re_escape_hint(self) -> None:
+        with pytest.warns():
+            with pytest.raises(pytest.fail.Exception) as excinfo:
+                with pytest.warns(UserWarning, match="foo (bar)"):
+                    warnings.warn("foo (bar)", UserWarning)
+        assert "re.escape()" in str(excinfo.value)
+
+    def test_warns_match_re_escape_hint_no_false_positive(self) -> None:
+        with pytest.warns():
+            with pytest.raises(pytest.fail.Exception) as excinfo:
+                with pytest.warns(DeprecationWarning, match="foo (bar)"):
+                    warnings.warn("some deprecation msg", DeprecationWarning)
+                    warnings.warn("foo (bar)", UserWarning)
+        assert "re.escape()" not in str(excinfo.value)
+
     @pytest.mark.filterwarnings("ignore")
     def test_can_capture_previously_warned(self) -> None:
         def f() -> int:
@@ -589,7 +620,7 @@ def __init__(self, a, b):
             pass
 
     with pytest.warns(CustomWarning):
-        with pytest.raises(pytest.fail.Exception, match="DID NOT WARN"):
+        with pytest.raises(pytest.fail.Exception, match="Regex pattern did not match"):
             with pytest.warns(CustomWarning, match="not gonna match"):
                 a, b = 1, 2
                 warnings.warn(CustomWarning(a, b))