clustering unit test

[toon-vc]

My second attempt to add the clustering unit test. If this is successful, I will close the other pull request and remove the 'clustering' branch.

[codecov-io]

Codecov Report

Merging #348 into develop will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@## develop #348 +/- ##
========================================
Coverage 89.69% 89.69% ========================================
Files 32 32 Lines 2522 2522 ========================================
Hits 2262 2262 Misses 260 260

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[mfeurer]

Looks good, but you may want to add a pipeline unit test, too?