Tested on python 3.5 and 3.7
We make light use of pyenv to set an appropriate python version if
installed. We could easily install a correct version too if we wanted
but that seemed invasive.
The newer ruamel was an annoying upgrade but also offers some
improvements that exposed some test suite issues (fixed later).
We add a new pytest flag `--accept` that will automatically write back
yaml files with updated responses. This makes it much easier and less
error-prone to update test cases when we expect output to change, or
when authoring new tests.
Second we make sure to test that we actually preserve the order of the
selection set when returning results. This is a "SHOULD" part of the
spec but seems pretty important and something that users will rely on.
To support both of the above we use ruamel.yaml which preserves a
certain amount of formatting and comments (so that --accept can work in
a failry ergonomic way), as well as ordering (so that when we write yaml
the order of keys has meaning that's preserved during parsing).
Use ruamel.yaml everywhere for consistency (since both libraries have
different quirks).
Quirks of ruamel.yaml:
- trailing whitespace in multiline strings in yaml files isn't written
back out as we'd like: https://bitbucket.org/ruamel/yaml/issues/47/multiline-strings-being-changed-if-they
- formatting is only sort of preserved; ruamel e.g. normalizes
indentation. Normally the diff is pretty clean though, and you can
always just check in portions of your test file after --accept
fixup
