improve error msg and test

Author: reaganjlee

src/_pytest/assertion/util.py

@@ -136,7 +136,10 @@ def isiterable(obj: Any) -> bool:
  return False
  except Exception as e:
  raise ValueError(
- f"Unexpected exception {e!r} while testing object {obj!r}. Probably an issue with __iter__"
+ [
+ f"pytest_assertion plugin: unexpected exception {e!r} while testing object {obj!r}",
+ ", probably from __iter__",
+ ]
  )
 
 
@@ -203,9 +206,9 @@ def assertrepr_compare(
  if (
  isinstance(e, ValueError)
  and (len(e.args) == 1)
- and ("Unexpected exception" in str(e.args[0]))
+ and ("__iter__" in str(e.args[0]))
  ):
- explanation = [e.args[0]]
+ explanation = e.args[0]
  else:
  explanation = [
  "(pytest_assertion plugin: representation of details failed: {}.".format(

testing/test_assertrewrite.py

@@ -698,7 +698,7 @@ def __eq__(self, o: object) -> bool:
 
  msg = getmsg(f)
  assert msg is not None
- assert "Unexpected exception" in msg
+ assert "__iter__" in msg and "__repr__" not in msg
 
  def test_formatchar(self) -> None:
  def f() -> None: