Example test in math.md isn't in the code examples

[ruthmoog]

line 1013 TestSVGWriterAtMidnight isn't in the code examples in 7C
https://github.com/quii/learn-go-with-tests/blob/main/math/v7c/clockface/clockface_acceptance_test.go

It's a bit confusing, and the examples also seem to be out of sync in other places in this chapter.