check for user-generated exceptions

src/_pytest/assertion/util.py

@@ -132,8 +132,14 @@ def isiterable(obj: Any) -> bool:
     try:
         iter(obj)
         return not istext(obj)
-    except TypeError:
+    except Exception as e:
+        if (
+            isinstance(e, TypeError)
+            and (len(e.args) == 1)
+            and "iter() returned non-iterator of type" in str(e.args[0])
+        ):
             return False
+        raise ValueError(f"Unexpected exception {e!r} while testing object {obj!r}")
 
 
 def has_default_eq(
@@ -195,7 +201,14 @@ def assertrepr_compare(
                 explanation = _notin_text(left, right, verbose)
     except outcomes.Exit:
         raise
-    except Exception:
+    except Exception as e:
+        if (
+            isinstance(e, ValueError)
+            and (len(e.args) == 1)
+            and ("Unexpected exception" in str(e.args[0]))
+        ):
+            explanation = [e.args[0]]
+        else:
             explanation = [
                 "(pytest_assertion plugin: representation of details failed: {}.".format(
                     _pytest._code.ExceptionInfo.from_current()._getreprcrash()