Randomly failing test cases

[ralf-meyer]

There are two test cases that cause "random" failures of the test suite

• test_bidentate (specifically smi4)
• test_example_7_no_FF

My guess is that for both these cases the problem comes from smiles to 3d geometry generation done using openbabel. Unfortunately, there is no way of providing a random seed (see issue #99) which leads to occasional "bad" structures and failures of the test case.

I recommend removing these until a better solution is found as these random failures of the test pipeline are extremely annoying during development.