Implement unit tests for pipeline element 'BooleanFilterProcessor'

[bossenti]

This issue is about implementing unit tests for our pipeline element BooleanFilterProcessor.
An example of how to write unit tests for pipeline elements can be found here.

Mentoring

As this issue is marked as a good first issue and for the hacktoberfest event: one of @dominikriemer, @tenthe, @RobertIndie, or @bossenti are happy to provide help for getting started, just tag (one of) them if you want to start working on this issue and need some help.

[muyangye]

Can someone please assign this issue to me? I know I am not a first time contributor but I have never worked on unit test before. I believe this will give me a more well-rounded understanding of the project. Thanks!

[bossenti]

Awesome, @muyangye!
good first issues are not intended to be exclusive for first-time contributors but are especially appropriate 🙂
So feel always free to catch them

[muyangye]

Hi I have pushed a PR that unit tests BooleanFilterProcessor. 2 quick concerns I have:

• Does the directory structure seem good? Since no one has written any unit tests for module streampipes-processors-filters-jvm yet, I followed the directory structure convention of module streampipes-processors-transformation-jvm and created some new packages. I am not sure so please let me know the correct directory structure.
• In order to test all filter processors, one needs to be able to tell the number of events being filtered. However, because SpOutputCollector is just an interface, one must define a class that implements the interface so that he can get the number of events. I followed the class in this test and I think other developers implementing unit tests for filter processors will probably do the same. Do you think it's a good idea to extract this class to make it commonly usable?

[bossenti]

Thanks for your contribution @muyangye

I am not sure so please let me know the correct directory structure.

The structure you have created is totally fine and exactly what I would have expected

Do you think it's a good idea to extract this class to make it commonly usable?

Yes, this would be great! How about putting it into streampipes-test-utils creating a package called org.apache.streampipes.test.extensions.api? (cc @dominikriemer)

[muyangye]

Thanks for the suggestion @bossenti! I just pushed an update that:

• Created the new package
• Refactored TestChangedValueDetectionProcessor