FYI, I just created a PR to add one more test to the prior fix, to test a slightly different aspect.

Whereas the test in the first PR checks that exc.__context__ is set after gen.throw() is finished, the new test checks that exc.__context__ is available also from within the generator (while the generator is running). I'm adding this test partly because this behavior is different from the "awaiting on a task" case, which I'm working on next.

Both of these tests were failing prior to the fix, which I confirmed.