[test] Add check for BCRSMatrix::nonzeroes()

Carsten Gräserrequested to merge
feature/test-bcrsmatrix-nnz into master

This adds a check for BCRSMatrix::nonzeroes() which reveals the problem of #28 (closed). The test currently fails for random build-mode and for row_wise build-mode with non-given nnz. This should be merged once #28 (closed) is fixed.

Edited by Martin Nolte

Merge request reports