Testing without rendering webpages

[roed314]

Almost all of the current testing the LMFDB is of the form

1. Create a webpage
2. Search for strings in the resulting html

While this is good for ensuring that our core product is functional, it has a cost in that rendering pages is somewhat slow. This makes certain kinds of automated tests not a good idea (we already have to split our testing up into a bunch of different jobs on Github's CI).

There are other kinds of tests that we can add, where we run unit tests on functions without rendering a webpage. For example, see this test I just added in #6248. To be specific, I think we should

1. Add tests for many of the functions in the lmfdb.utils folder
2. Add tests for the methods on backend objects like WebAbstractGroup.