How is that ambiguous? The best interpretation I can find where "test" is a verb is an elision: Test [that] B is an alternative to test A. That is an unlikely reading: "test" is a verb in the first instance and a noun in the second, breaking parallelism. And it's just a very unlikely thing to direct someone to do.

"Test B is an alternative to test A."

could mean there's a Test B and a Test A, and they're interchangeable.

Or:

You can run Test B to confirm A works, that is "to test A".

Again the stated goal to clear documentation for non-native or limited-exposure speakers. This doesn't pass that test.

Ah, I see, taking "to test A" as an infinitive. But it would be strange to say test B is an alternative without saying what it's an alternative to. The other reading still seems quite unlikely.

The point of STE100 is to avoid ambiguity like this, though.

The point of STE is to support technical writers who have knowledge of the matter and a style guide. In other words, STE will not make something unambiguous simply by replacing words. The example sentence is just to illustrate a grammar rule: "test" as a verb vs a noun. That is all. You should not assume an STE rule will disambiguate a single sentence pulled out of context.