message: Add comments explaining why the test is skipped for f16
diff: @@ -52,6 +52,7 @@ class AdamOptimizerTest(XLATestCase):
  def testBasic(self):
  for dtype in self.float_types:
  + # TODO: test fails for float16 due to excessive precision requirements.
  if dtype == np.float16:
  continue
  with self.test_session(), self.test_scope():
  @@ -93,6 +94,7 @@ class AdamOptimizerTest(XLATestCase):
  def testTensorLearningRate(self):
  for dtype in self.float_types:
  + # TODO: test fails for float16 due to excessive precision requirements.
  if dtype == np.float16:
  continue
  with self.test_session(), self.test_scope():
  @@ -134,6 +136,7 @@ class AdamOptimizerTest(XLATestCase):
  def testSharing(self):
  for dtype in self.float_types:
  + # TODO: test fails for float16 due to excessive precision requirements.
  if dtype == np.float16:
  continue
  with self.test_session(), self.test_scope():
  