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

@@ -1230,7 +1230,9 @@ 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 +1592,29 @@ def g():
             ]
         )
 
+    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()
+
+        r = excinfo.getrepr()
+        file = io.StringIO()
+        tw = TerminalWriter(file=file)
+        tw.hasmarkup = False
+        r.toterminal(tw)
+
+        output = file.getvalue()
+        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_cycle(self, importasmod, tw_mock):
         __tracebackhide__ = True
         mod = importasmod(