display single contained exception in excgroups in short test summary info

Author: jakkdl

changelog/12943.improvement.rst

@@ -0,0 +1 @@
+If a test fails with an exceptiongroup with a single exception, the contained exception will now be displayed in the short test summary info.

src/_pytest/_code/code.py

@@ -1033,6 +1033,24 @@ def _truncate_recursive_traceback(
 
     def repr_excinfo(self, excinfo: ExceptionInfo[BaseException]) -> ExceptionChainRepr:
         repr_chain: list[tuple[ReprTraceback, ReprFileLocation | None, str | None]] = []
+
+        def _get_single_subexc(
+            eg: BaseExceptionGroup[BaseException],
+        ) -> BaseException | None:
+            res: BaseException | None = None
+            for subexc in eg.exceptions:
+                if res is not None:
+                    return None
+
+                if isinstance(subexc, BaseExceptionGroup):
+                    res = _get_single_subexc(subexc)
+                    if res is None:
+                        # there were multiple exceptions in the subgroup
+                        return None
+                else:
+                    res = subexc
+            return res
+
         e: BaseException | None = excinfo.value
         excinfo_: ExceptionInfo[BaseException] | None = excinfo
         descr = None
@@ -1041,6 +1059,7 @@ def repr_excinfo(self, excinfo: ExceptionInfo[BaseException]) -> ExceptionChainR
             seen.add(id(e))
 
             if excinfo_:
+                reprcrash = excinfo_._getreprcrash()
                 # Fall back to native traceback as a temporary workaround until
                 # full support for exception groups added to ExceptionInfo.
                 # See https://github.com/pytest-dev/pytest/issues/9159
@@ -1054,9 +1073,13 @@ def repr_excinfo(self, excinfo: ExceptionInfo[BaseException]) -> ExceptionChainR
                             )
                         )
                     )
+                    if (
+                        reprcrash is not None
+                        and (subexc := _get_single_subexc(e)) is not None
+                    ):
+                        reprcrash.message = f"[in {type(e).__name__}] {subexc!r}"
                 else:
                     reprtraceback = self.repr_traceback(excinfo_)
-                reprcrash = excinfo_._getreprcrash()
             else:
                 # Fallback to native repr if the exception doesn't have a traceback:
                 # ExceptionInfo objects require a full traceback to work.

testing/code/test_excinfo.py

@@ -1703,6 +1703,63 @@ def test_exceptiongroup(pytester: Pytester, outer_chain, inner_chain) -> None:
     _exceptiongroup_common(pytester, outer_chain, inner_chain, native=False)
 
 
+def test_exceptiongroup_short_summary_info(pytester: Pytester):
+    pytester.makepyfile(
+        """
+        import sys
+
+        if sys.version_info < (3, 11):
+            from exceptiongroup import BaseExceptionGroup, ExceptionGroup
+
+        def test_base() -> None:
+            raise BaseExceptionGroup("NOT IN SUMMARY", [SystemExit("a" * 10)])
+
+        def test_nonbase() -> None:
+            raise ExceptionGroup("NOT IN SUMMARY", [ValueError("a" * 10)])
+
+        def test_nested() -> None:
+            raise ExceptionGroup(
+                "NOT DISPLAYED", [
+                    ExceptionGroup("NOT IN SUMMARY", [ValueError("a" * 10)])
+                ]
+            )
+
+        def test_multiple() -> None:
+            raise ExceptionGroup(
+                "b" * 10,
+                [
+                    ValueError("NOT IN SUMMARY"),
+                    TypeError("NOT IN SUMMARY"),
+                ]
+            )
+        """
+    )
+    result = pytester.runpytest("-vv")
+    assert result.ret == 1
+    result.stdout.fnmatch_lines(
+        [
+            "*= short test summary info =*",
+            (
+                "FAILED test_exceptiongroup_short_summary_info.py::test_base - "
+                "[in BaseExceptionGroup] SystemExit('aaaaaaaaaa')"
+            ),
+            (
+                "FAILED test_exceptiongroup_short_summary_info.py::test_nonbase - "
+                "[in ExceptionGroup] ValueError('aaaaaaaaaa')"
+            ),
+            (
+                "FAILED test_exceptiongroup_short_summary_info.py::test_nested - "
+                "[in ExceptionGroup] ValueError('aaaaaaaaaa')"
+            ),
+            (
+                "FAILED test_exceptiongroup_short_summary_info.py::test_multiple - "
+                "ExceptionGroup: bbbbbbbbbb (2 sub-exceptions)"
+            ),
+            "*= 4 failed in *",
+        ]
+    )
+
+
 @pytest.mark.parametrize("tbstyle", ("long", "short", "auto", "line", "native"))
 def test_all_entries_hidden(pytester: Pytester, tbstyle: str) -> None:
     """Regression test for #10903."""