Fix duplicated exception chain output when an exception group has a cause

changelog/14828.bugfix.rst

@@ -0,0 +1 @@
+Exception groups raised from another exception now print their cause chain only once in the traceback output.

src/_pytest/_code/code.py

@@ -1232,7 +1232,9 @@ def repr_excinfo(self, excinfo: ExceptionInfo[BaseException]) -> ExceptionChainR
                 reprcrash = None
             repr_chain.append((reprtraceback, reprcrash, description))
 
-            if e.__cause__ is not None and self.chain:
+            if isinstance(e, BaseExceptionGroup) and self.chain:
+                e = None
+            elif e.__cause__ is not None and self.chain:
                 e = e.__cause__
                 excinfo_ = ExceptionInfo.from_exception(e) if e.__traceback__ else None
                 description = "The above exception was the direct cause of the following exception:"

testing/code/test_excinfo.py

@@ -1592,6 +1592,66 @@ def g():
             ]
         )
 
+    def _render_output(self, excinfo: ExceptionInfo[BaseException]) -> str:
+        r = excinfo.getrepr()
+        file = io.StringIO()
+        tw = TerminalWriter(file=file)
+        tw.hasmarkup = False
+        r.toterminal(tw)
+        return file.getvalue()
+
+    def test_exc_chain_repr_exception_group_with_cause(self) -> None:
+        """An exception group raised from another exception must not print that
+        exception's cause chain twice."""
+        try:
+            try:
+                raise RuntimeError("original cause")
+            except RuntimeError as exc:
+                raise ExceptionGroup("group", [ValueError("inner")]) from exc
+        except ExceptionGroup:
+            excinfo = ExceptionInfo.from_current()
+
+        output = self._render_output(excinfo)
+        assert output.count("RuntimeError: original cause") == 1
+        assert output.count("ExceptionGroup: group") == 1
+        assert output.count("ValueError: inner") == 1
+        assert output.count("The above exception was the direct cause") == 1
+
+    def test_exc_chain_repr_exception_group_with_context(self) -> None:
+        """An exception group raised during handling must not print the
+        implicit context chain twice."""
+        exc1 = RuntimeError("implicit context")
+        try:
+            raise exc1
+        except RuntimeError as exc:
+            group = ExceptionGroup("group", [ValueError("inner")])
+            group.__context__ = exc
+        try:
+            raise group
+        except ExceptionGroup:
+            excinfo = ExceptionInfo.from_current()
+
+        output = self._render_output(excinfo)
+        assert output.count("RuntimeError: implicit context") == 1
+        assert output.count("During handling of the above exception") == 1
+
+    def test_exc_chain_repr_nested_exception_group_with_cause(self) -> None:
+        """A nested exception group raised from another exception must not
+        print the cause chain twice."""
+        try:
+            try:
+                raise RuntimeError("root cause")
+            except RuntimeError as exc:
+                raise ExceptionGroup(
+                    "outer", [ExceptionGroup("inner", [ValueError("v")])]
+                ) from exc
+        except ExceptionGroup:
+            excinfo = ExceptionInfo.from_current()
+
+        output = self._render_output(excinfo)
+        assert output.count("RuntimeError: root cause") == 1
+        assert output.count("The above exception was the direct cause") == 1
+
     def test_exc_chain_repr_without_traceback_multiple_links(self) -> None:
         """
         Exceptions without a traceback that are themselves part of a longer
@@ -1613,13 +1673,7 @@ def test_exc_chain_repr_without_traceback_multiple_links(self) -> None:
         except ValueError:
             excinfo = ExceptionInfo.from_current()
 
-        r = excinfo.getrepr()
-        file = io.StringIO()
-        tw = TerminalWriter(file=file)
-        tw.hasmarkup = False
-        r.toterminal(tw)
-
-        output = file.getvalue()
+        output = self._render_output(excinfo)
         for message in (
             "ValueError: abcd",
             "IndexError: efgh",
@@ -1648,13 +1702,7 @@ def test_exc_chain_repr_mixed_traceback(self) -> None:
         except ValueError:
             excinfo = ExceptionInfo.from_current()
 
-        r = excinfo.getrepr()
-        file = io.StringIO()
-        tw = TerminalWriter(file=file)
-        tw.hasmarkup = False
-        r.toterminal(tw)
-
-        output = file.getvalue()
+        output = self._render_output(excinfo)
         assert output.count("ValueError: outer without traceback") == 1
         assert output.count("RuntimeError: inner with traceback") == 1
         assert output.count("The above exception was the direct cause") == 1

testing/test_unittest.py

@@ -1609,7 +1609,7 @@ def test(self):
         result.stdout.fnmatch_lines(
             [
                 "* ERROR at setup of MyTestCase.test *",
-                "E * Exception: fail 0",
+                "*Exception: fail 0",
             ]
         )