Interesting. I added 10 “not” tests, and sure enough, a lot of the tests that were passing were not passing for the reason I had thought they were.
Changing the "find"s to “exists” fixed most, except for four of them.
I changed the first problem test to an “equals” and discovered that although I specified currentUser as “TestRunner” instead of “Welcome TestRunner” it was “Welcome eviltrout”.
This apparently is coming from a fixture.
I don’t know if having plugins test against Core test fixtures is a great idea, but I guess it could work. Better would be for me to learn how to use my own fixtures that would be part of the plugin.