BUG: fix tests

some test always fail on the server side, whereas local tests pass. Find the source and solve the problem

added Doing bug labels

solved by reordering the tests order. There was a problem, when the next generator was called before a test with getitem method. Somehow the next generator object wasn't closed properly

mentioned in commit 22382091

added 1h 40m of time spent at 2019-11-28

added merged in Develop label and removed Doing label

closed via merge request !17 (merged)

mentioned in commit 1f2c0182