Which files suffer from a complete lack of tests?

[Artur Malabarba]

I'm trying to add some tests for features (.el source files) that are completely devoid of them. So I welcome suggestions of elisp files that have no tests whatsoever. I also welcome volunteers to help, of course.

Context:
Besides the fact that tests are a good idea, I think that having features with no test file at all is measurably worse than having just one or two tests.

When a source file has no corresponding test file, someone contributing to it feels perfectly entitled to not create one. What's worse, even if they did want to add a test, there's a chance they might be discouraged by this, specially if they weren't yet sure how to implement the test.

So it is my opinion that adding tests to these unfortunate files would provide a bit more benefit for the effort invested.

Best,
Artur