message: Use assertLen to avoid linter complaining
diff: @@ -375,12 +375,12 @@ class RegroupAndSelectDeviceTest(test.TestCase):
  def testNested(self):
  result = values.regroup((_nested_value("1"), _nested_value("2")))
  self.assertIsInstance(result, tuple)
  - self.assertEqual(3, len(result))
  + self.assertLen(result, 3)
  self._is_per_replica(result[0], ["a1", "a2"])
  self._is_per_replica(result[2], ["h1", "h2"])
  self.assertIsInstance(result[1], list)
  - self.assertEqual(3, len(result[1]))
  + self.assertLen(result[1], 3)
  self._is_per_replica(result[1][0], ["b1", "b2"])
  self._is_per_replica(result[1][2], ["g1", "g2"])
  @@ -416,12 +416,12 @@ class RegroupAndSelectDeviceTest(test.TestCase):
  result = values.regroup((_nested_value("1"), _nested_value("2")),
  values.Mirrored)
  self.assertIsInstance(result, tuple)
  - self.assertEqual(3, len(result))
  + self.assertLen(result, 3)
  self._is_per_replica(result[0], ["a1", "a2"], values.Mirrored)
  self._is_per_replica(result[2], ["h1", "h2"], values.Mirrored)
  self.assertIsInstance(result[1], list)
  - self.assertEqual(3, len(result[1]))
  + self.assertLen(result[1], 3)
  self._is_per_replica(result[1][0], ["b1", "b2"], values.Mirrored)
  self._is_per_replica(result[1][2], ["g1", "g2"], values.Mirrored)
  @@ -444,7 +444,7 @@ class RegroupAndSelectDeviceTest(test.TestCase):
  def testWrapAListOfTwoTuples(self):
  result = values.regroup([("1", "2"), ("3", "4")])
  self.assertIsInstance(result, tuple)
  - self.assertEqual(2, len(result))
  + self.assertLen(result, 2)
  self._is_per_replica(result[0], ("1", "3"), values.PerReplica)
  self._is_per_replica(result[1], ("2", "4"), values.PerReplica)
  @@ -459,19 +459,19 @@ class RegroupAndSelectDeviceTest(test.TestCase):
  foo = object()
  result = values.regroup((("a", foo), ("b", foo)))
  self.assertIsInstance(result, tuple)
  - self.assertEqual(2, len(result))
  + self.assertLen(result, 2)
  self._is_per_replica(result[0], ["a", "b"])
  self.assertIs(foo, result[1])
  # Test select_replica(), should undo the merge done by regroup().
  result_0 = values.select_replica(0, result)
  self.assertIsInstance(result_0, tuple)
  - self.assertEqual(2, len(result_0))
  + self.assertLen(result_0, 2)
  self.assertEqual("a", result_0[0])
  self.assertIs(foo, result_0[1])
  result_1 = values.select_replica(1, result)
  self.assertIsInstance(result_1, tuple)
  - self.assertEqual(2, len(result_1))
  + self.assertLen(result_1, 2)
  self.assertEqual("b", result_1[0])
  self.assertIs(foo, result_1[1])
  