Describe the bug

The coverage tool NYC yarn test:nyc produces output that doesn't comport with reality.

To Reproduce

checkout on master, running in packages/zoe:

yarn test:nyc
produces

Expected behavior

I was a little suspicious of the last line, on zoeSeat.js. I set breakpoints on every basic block, and a few other lines, then ran under the debugger (in WebStorm, but your results should be consistent in any debugger.) I ran the tests test-zoeHelpersWZcf.js, and test-zcf.js, and hit every single breakpoint I had set.

Also notice that the line numbers given as "uncovered" in zoe.js mostly don't correspond to actual code.