Add more tests for the html report

[handwerkerd]

Summary

The functions that generates the html reports have almost no testing coverage. No one is actively working on that code, but if more visualizations of outputs might be added once the decision tree modularization #756 is merged, then it might be useful to have a bit more of a testing framework in place there.

Additional Detail

There currently only one test for one small aspect of the reports: https://github.com/ME-ICA/tedana/blob/f00cb25152142611b8e289ab59c7b5b8ab6eaf08/tedana/tests/test_reporting.py#L9

Next Steps

• Decide how much of a priority this is
• Add some tests

[tsalo]

We use Jinja, right? There might be some good testing examples out there for templating tools.