Olaf created KAFKA-12296:
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Summary: MockProducer behaves contrary to documentation of Callback
Key: KAFKA-12296
URL: https://issues.apache.org/jira/browse/KAFKA-12296
Project: Kafka
Issue Type: Bug
Components: producer , unit tests
Affects Versions: 2.7.0
Reporter: Olaf
In Unit tests, a MockProducer is used to imitate a real producer.
Using the errorNext(RuntimeException e) method, it is possible to indicate
failures.
BUT: the asynchronous send method with a callback has a clear documentation of
that callback interface, stating that Metadata will always be set, and never
null.
{{The metadata for the record that was sent (i.e. the partition and offset). An
empty metadata with -1 value for all fields except for topicPartition will be
returned if an error occurred.}}
The bug is, that in MockProducer's Completion implementation the following
happens:
{{if (e == null)}}
{{ callback.onCompletion(metadata, null);}}
{{else}}
{{ callback.onCompletion(null, e);}}
Behaving against the own documentation lead to a very subtle bug: tests that
implement the error condition checking metadata != null will be fine, but in
real life fail horribly.
A MockProducer should at all times behave exactly like the real thing and
adhere to the documentation of the Callback!
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