Add unit tests for pipeline elements

[bossenti]

Body

Our pipeline elements lack proper unit tests. This is something we should improve. This issue collects pipeline elements that need (more) unit tests. Dedicated sub-issues are created for the implementation of each pipeline element.

Pipeline elements to be improved:

• [ ] #1885
• [ ] #1886
• [ ] #1887
• [x] #1888
• [ ] #1889
• [ ] #1890
• [x] #1891
• [x] #1892
• [ ] #1893
• [ ] #1894
• [x] #1895
• [ ] #1896
• [ ] #1897
• [ ] #1898
• [ ] #1899
• [ ] #1900
• [x] #1901
• [x] #1902
• [ ] #1903
• [ ] #1904

StreamPipes Committer

I acknowledge that I am a maintainer/committer of the Apache StreamPipes project.

[aamirxshaikh]

hey @bossenti I'm really interested in contributing to these issues.

[bossenti]

That's great to hear @aamirxshaikh Simply pick one of the tasks and add a comment there so I can assign you to it