refactor tests that rely on saved data

[zkamvar]

There are currently a lot of tests that rely on saved data structures. These are inherently fragile and should be thoroughly tested before any other changes are made to the codebase (especially efforts like #83).

Because this package is being used A LOT in the field, it's important to make sure that we have a sufficient depth of coverage for our tests so that we fight code rot.

[thibautjombart]

+1 to this!