enhance rec-warn error

src/_pytest/recwarn.py

@@ -268,15 +268,19 @@ def __exit__(
 
         __tracebackhide__ = True
 
+        def found_str():
+            found = "".join(f"  {each.message!r},\n" for each in self)
+            return f"\n{found}" if found else ""
+
         # only check if we're not currently handling an exception
         if exc_type is None and exc_val is None and exc_tb is None:
             if self.expected_warning is not None:
                 if not any(issubclass(r.category, self.expected_warning) for r in self):
                     __tracebackhide__ = True
                     fail(
-                        "DID NOT WARN. No warnings of type {} was emitted. "
-                        "The list of emitted warnings is: {}.".format(
-                            self.expected_warning, [each.message for each in self]
+                        "DID NOT WARN. No warnings of type {expected} was emitted. "
+                        "The list of emitted warnings is: [{found}].".format(
+                            expected=self.expected_warning, found=found_str()
                         )
                     )
                 elif self.match_expr is not None:
@@ -286,11 +290,13 @@ def __exit__(
                                 break
                     else:
                         fail(
-                            "DID NOT WARN. No warnings of type {} matching"
-                            " ('{}') was emitted. The list of emitted warnings"
-                            " is: {}.".format(
-                                self.expected_warning,
-                                self.match_expr,
-                                [each.message for each in self],
+                            "DID NOT WARN. No warnings of type {expected} matching the"
+                            " regex was emitted.\n"
+                            "The regex is: {match!r}\n"
+                            "The list of emitted warnings"
+                            " is: [{found}].".format(
+                                expected=self.expected_warning,
+                                match=self.match_expr,
+                                found=found_str(),
                             )
                         )

testing/test_recwarn.py

@@ -1,4 +1,3 @@
-import re
 import warnings
 from typing import Optional
 
@@ -251,23 +250,25 @@ def test_as_contextmanager(self) -> None:
         with pytest.raises(pytest.fail.Exception) as excinfo:
             with pytest.warns(RuntimeWarning):
                 warnings.warn("user", UserWarning)
-        excinfo.match(
+        assert excinfo.match(
             r"DID NOT WARN. No warnings of type \(.+RuntimeWarning.+,\) was emitted. "
-            r"The list of emitted warnings is: \[UserWarning\('user',?\)\]."
+            r"The list of emitted warnings is: \[\n"
+            r"  UserWarning\('user'\),\n"
+            r"\]."
         )
 
         with pytest.raises(pytest.fail.Exception) as excinfo:
             with pytest.warns(UserWarning):
                 warnings.warn("runtime", RuntimeWarning)
-        excinfo.match(
+        assert excinfo.match(
             r"DID NOT WARN. No warnings of type \(.+UserWarning.+,\) was emitted. "
-            r"The list of emitted warnings is: \[RuntimeWarning\('runtime',?\)\]."
+            r"The list of emitted warnings is: \[\n  RuntimeWarning\('runtime',?\),\n\]."
         )
 
         with pytest.raises(pytest.fail.Exception) as excinfo:
             with pytest.warns(UserWarning):
                 pass
-        excinfo.match(
+        assert excinfo.match(
             r"DID NOT WARN. No warnings of type \(.+UserWarning.+,\) was emitted. "
             r"The list of emitted warnings is: \[\]."
         )
@@ -280,14 +281,11 @@ def test_as_contextmanager(self) -> None:
 
         message_template = (
             "DID NOT WARN. No warnings of type {0} was emitted. "
-            "The list of emitted warnings is: {1}."
+            "The list of emitted warnings is: [\n{1}]."
         )
-        excinfo.match(
-            re.escape(
-                message_template.format(
-                    warning_classes, [each.message for each in warninfo]
-                )
-            )
+
+        assert str(excinfo.value) == message_template.format(
+            warning_classes, "".join(f"  {each.message!r},\n" for each in warninfo)
         )
 
     def test_record(self) -> None: