test(expenses): refactor tests for graphql expenses
test(expenses): refactor tests for graphql expenses

This refactoring has two purposes:

 1) I've been chasing some bugs related to `beforeEach` hooks failing
    because pieces of previous tests are still running and interfering
    with the current tests. Since I found a small set of tests in the
    expense suite that allowed me to reproduce the error in ~20s
    consistently, I decided to look carefully into the code while I
    worked on these tests.  More about that in the next commit.

 2) I'm working on the feature 1030* and I wanted to learn more about
    how expenses and payment methods worked (I guess it's the first
    time I touch this code)

 3) I'm using this feature as the test bed for issue 1048* and
    proposing a new standard took some more TLC on the readability

 *) Bonus: all the `console.log` calls were removed on tests that
    expect the graphql calls to fail. Which means that we still have
    those calls for debugging when something unexpected happens, but
    we don't have all the noise of expected exceptions showing up on
    the test output.

*1030: https://github.com/opencollective/opencollective/issues/1030
*1048: https://github.com/opencollective/opencollective/issues/1048

OpenCollective/opencollective-api,OpenCollective/opencollective-api,OpenCollective/opencollective-api