tests: use assertTrue() instead of assert_() in test-bdiff.py

The later is deprecated in Python 3.

This patch also makes the test pass on Python 3.

Differential Revision: https://phab.mercurial-scm.org/D4697

contrib/python3-whitelist

@@ -22,6 +22,7 b' test-backout.t'
 test-backwards-remove.t
 test-bad-pull.t
 test-basic.t
+test-bdiff.py
 test-bheads.t
 test-bisect.t
 test-bisect2.t

tests/test-bdiff.py

@@ -99,7 +99,7 b' class BdiffTests(unittest.TestCase):'
                      diffreplace(12, 12, b'', b'b\nc\n.\n'),
                      b'd\ne\n',
                      diffreplace(16, 18, b'.\n', b''), b'f\n']
-        self.assert_(got in (want_c, want_pure),
+        self.assertTrue(got in (want_c, want_pure),
                      'got: %r, wanted either %r or %r' % (
                          got, want_c, want_pure))