Spruce tests

Hi, Antonio.

This makes a few minor revisions to the tests in marvelite. I suppress a warning, fix a few typos, make endpoints more explicit, and update the method names in the series tests to match the actual method names in use.

Awesome gem! Really cool to see how others implement API wrappers.

Cheers,
O-I
Line is too long. [89/80]<br>Prefer double-quoted strings unless you need single quotes to avoid extra backslashes for escaping.