Xiao Wang created LOG4J2-3164:
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Summary: Refactor StoringStatusListener to improve test logic
Key: LOG4J2-3164
URL: https://issues.apache.org/jira/browse/LOG4J2-3164
Project: Log4j 2
Issue Type: Improvement
Components: Core
Reporter: Xiao Wang
h3. Description
I noticed that there is a test class
[StoringStatusListener|https://github.com/apache/logging-log4j2/blob/20f9a97dbe5928c3b5077bcdd2a22ac92e941655/log4j-core/src/test/java/org/apache/logging/log4j/core/config/plugins/validation/validators/ValidatingPluginWithFailoverTest.java#L86]
implements production interface
[StatusListener|https://github.com/apache/logging-log4j2/blob/20f9a97dbe5928c3b5077bcdd2a22ac92e941655/log4j-api/src/main/java/org/apache/logging/log4j/status/StatusListener.java#L27]
to assist testing
[PluginBuilder.build()|https://github.com/apache/logging-log4j2/blob/20f9a97dbe5928c3b5077bcdd2a22ac92e941655/log4j-core/src/main/java/org/apache/logging/log4j/core/config/plugins/util/PluginBuilder.java#L117].
This might not be the best priactice in unit testing and can be improved by
leveraging mocking frameworks.
h3. Current Implementation
* {{StoringStatusListener}} implements {{StatusListener}} and overrides
methods to track the input parameters of {{StatusListener.log(StatusData)}}.
* In test case, the child test class is used in assertion statement to make
sure the log method never been executed.
h3. Proposed Implementation
* Replace {{StoringStatusListener}} with a mocking object created by Mockito.
* Use method stub to control the behavior of {{getStatusLevel()}}.
* Use {{ArgumentCapture}} to capture the input argument for
{{StatusListener.log(StatusData)}} and use it in the assertion statement.
h3. Motivation
* Decouple test class {{StoringStatusListener}} from production interface
{{StatusListener}}.
* Remove the redundant test child class {{StoringStatusListener}}
* Remove the redundant overridden methods {{close()}}
* Make testing logic more explict by directly verify the input argument
through ArgumentCapture.
h3. More Thought
* If we only want to make sure that the {{log(StatusData)}} method was never
been executed, we can verify it by {{Mockito.times()}} and get rid of the
ArgumentCapture. It can make the test condition even more clear.
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