terminal: summary_errors: replace if with assert

Author: blueyed

src/_pytest/terminal.py

@@ -851,7 +851,8 @@ def summary_errors(self):
                     msg = "ERROR collecting " + msg
                 elif rep.when == "setup":
                     msg = "ERROR at setup of " + msg
-                elif rep.when == "teardown":
+                else:
+                    assert rep.when == "teardown", "Unexpected rep: %r" % (rep,)
                     msg = "ERROR at teardown of " + msg
                 self.write_sep("_", msg, red=True, bold=True)
                 self._outrep_summary(rep)