enhance rec-warn error

* uses multiple lines for found warnings

Author: RonnyPfannschmidt

src/_pytest/recwarn.py

@@ -136,7 +136,7 @@ def warns(
         ...     warnings.warn("this is not here", UserWarning)
         Traceback (most recent call last):
           ...
-        Failed: DID NOT WARN. No warnings of type ...UserWarning... was emitted...
+        Failed: DID NOT WARN. No warnings of type ...UserWarning... were emitted...
 
     """
     __tracebackhide__ = True
@@ -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} were 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
 
@@ -263,16 +262,18 @@ def test_as_contextmanager(self) -> None:
             with pytest.warns(RuntimeWarning):
                 warnings.warn("user", UserWarning)
         excinfo.match(
-            r"DID NOT WARN. No warnings of type \(.+RuntimeWarning.+,\) was emitted. "
-            r"The list of emitted warnings is: \[UserWarning\('user',?\)\]."
+            r"DID NOT WARN. No warnings of type \(.+RuntimeWarning.+,\) were emitted. "
+            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(
             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:
@@ -289,18 +290,14 @@ def test_as_contextmanager(self) -> None:
                 warnings.warn("runtime", RuntimeWarning)
                 warnings.warn("import", ImportWarning)
 
-        message_template = (
-            "DID NOT WARN. No warnings of type {0} was emitted. "
-            "The list of emitted warnings is: {1}."
-        )
-        excinfo.match(
-            re.escape(
-                message_template.format(
-                    warning_classes, [each.message for each in warninfo]
-                )
-            )
+        messages = "".join(f"  {each.message!r},\n" for each in warninfo)
+        expected_str = (
+            f"DID NOT WARN. No warnings of type {warning_classes} was emitted. "
+            f"The list of emitted warnings is: [\n{messages}]."
         )
 
+        assert str(excinfo.value) == expected_str
+
     def test_record(self) -> None:
         with pytest.warns(UserWarning) as record:
             warnings.warn("user", UserWarning)