[2.7] bpo-34031: fix incorrect usage of self.fail in two tests (GH-8091) (#8225)

Actually just one fix on the 2.7 branch.

Contributed by Bradley Laney.

(cherry picked from commit 6b490b5)

Author: taleinat

Lib/test/test_file.py

@@ -247,8 +247,7 @@ def testIteration(self):
         # Test for appropriate errors mixing read* and iteration
         for methodname, args in methods:
             f = self.open(TESTFN, 'rb')
-            if next(f) != filler:
-                self.fail, "Broken testfile"
+            self.assertEqual(next(f), filler)
             meth = getattr(f, methodname)
             meth(*args)  # This simply shouldn't fail
             f.close()