Re-enable the arithmetic optimizer by default in tests.

Add a warning to not disable optimizers without consulting with the Grappler team.

PiperOrigin-RevId: 215584369

tensorflow/python/framework/test_util.py

@@ -1992,10 +1992,12 @@ class TensorFlowTestCase(googletest.TestCase):
       # Don't perform optimizations for tests so we don't inadvertently run
       # gpu ops on cpu
       config.graph_options.optimizer_options.opt_level = -1
+      # Disable Grappler constant folding since some tests & benchmarks
+      # use constant input and become meaningless after constant folding.
+      # DO NOT DISABLE GRAPPLER OPTIMIZERS WITHOUT CONSULTING WITH THE
+      # GRAPPLER TEAM.
       config.graph_options.rewrite_options.constant_folding = (
           rewriter_config_pb2.RewriterConfig.OFF)
-      config.graph_options.rewrite_options.arithmetic_optimization = (
-          rewriter_config_pb2.RewriterConfig.OFF)
       config.graph_options.rewrite_options.pin_to_host_optimization = (
           rewriter_config_pb2.RewriterConfig.OFF)
       return config

tensorflow/python/kernel_tests/distributions/laplace_test.py

@@ -275,8 +275,8 @@ class LaplaceTest(test.TestCase):
     self.assertAllClose(
         sample_values.var(axis=0),
         stats.laplace.var(loc_bc, scale=scale_bc),
-        rtol=0.10,
-        atol=0.)
+        rtol=0.105,
+        atol=0.0)
     fails = 0
     trials = 0
     for ai, a in enumerate(np.reshape(loc_v, [-1])):