PR Summary

Use

fig, ax = plt.subplots()

instead of

fig = plt.figure()ax = plt.subplots(1, 1, 1)

The latter was a common pattern in tests. The former is shorter and thus adds less clutter to the tests.

More similar patterns could be replaced, but that's for another time.

Also fixed here along the way:

• One test that usedplt.errorbar instead ofax.errorbar - we should test using the OOP API unless we want to test pyplot specifically.
• Some copy-paste errors in comments.