Flaky tests

[dgasmith]

Describe the bug
Pubchem tests occasionally fail on CI.

Expected behavior
Pubchem tests should always pass to ensure CI is stable.

Additional context

We could consider a pytest wrapper like the following:

@pytest.mark.flaky(reruns=5)
def test_example():
    import random
    assert random.choice([True, False])

From this pytest module. Not an overwhelming fan of adding a new test depends, but could help. Also we could make with an xfail, but I feel this is dangerous.

[loriab]

When pubchem gets busy, it tends to be for a spell longer than the qcel tests, so rerun in quick succession may not help.

[dgasmith]

@mattwelborn Maybe time for mock...?

[loriab]

Before anyone spends more real time on that unfortunate file, may also want to consider pubchempy.

[dgasmith]

I would be up for copying pubchempys single file include with the license as the header.