prevented flaky behavior in graph mode for serial_ops.py by preemptively raising an exception if graph mode is detected.

Author: markemus

tensorflow_io/core/python/experimental/serial_ops.py

@@ -156,6 +156,10 @@ def dataset_to_examples(ds):
     WARNING: Only compatible with "dictionary-style" datasets {key: val, key2:val2,..., keyN, valN}.
     WARNING: Must run in eager mode!"""
     # TODO handle tuples and flat datasets as well.
+
+    if not tf.executing_eagerly():
+        raise ValueError("dataset_to_examples() must run in eager mode!")
+
     for x in ds:
         # Each individual tensor is converted to a known serializable type.
         features = {key: np_value_to_feature(value.numpy()) for key, value in x.items()}

tests/test_serial_ops.py

@@ -84,5 +84,5 @@ def graph_save_fail():
 
 def test_ensure_graph_fail():
     """Test that super_serial fails in graph mode."""
-    with pytest.raises(tf.errors.NotFoundError):
+    with pytest.raises(ValueError):
         graph_save_fail()