.when() context is inconsistent

[DaddyWarbucks]

Describe the bug
When using the third argument of .when() (aka testContext), the transform does not run as expected. Specifically I am trying to use the testContext.index of an array schema to access items retrieved from the when.

To Reproduce
I cannot, to save my life, figure out how to open the test panel on Codesandbox. I also was pulling my hair out because Codesandbox was running the code twice and this error is so weird in general. Instead I used StackBlitz. To access the console, inspect the page and it will bring up a separate Chrome DevTools (not embedded like Codesandbox).

https://stackblitz.com/edit/vitejs-vite-r7lfvf?file=main.js

Switch between commenting lines 11 and 14. Although both of these lines of code should do the exact same thing, line 11 does not work.

Expected behavior
I can use the testContext.index to retrieve things from context.

Platform (please complete the following information):

• Browser: Chrome
• Version: 1.4

Additional context
I am happy to work on this and can open a PR. But I am unclear on where to even start.