react’s own tests often (need to) look funny 
if you’re curious, i’m trying to fix this bug in react. it comes up when using code splitting with react router <Switch> and other cases. it’s been reported a while ago. it’s easy to work around so it wasn’t urgent but i wanted to look into it for a while. github.com/facebook/react…
the submitter of the issue was kind enough to send a pull request with a minimal failing test encapsulating the issue. this alone has significantly increased the chances that i would be able to find the bug. (when in doubt, send a failing test!) github.com/facebook/react…
there was also a community PR that attempts to solve the problem. it solves the bug. but i was hesitant because it fixes the main symptom, whereas i was concerned there has to be a deeper problem and some internal assumption led to this bug being possible. github.com/facebook/react…
i put a bunch of console logs in the code and investigated, trying to understand the original assumptions. i narrowed it down to a loop that seems to exit too early. it took me a few attempts but thanks to @acdlite’s tips i think i have a fix that works github.com/facebook/react…
initially i didn’t understand the code quite correctly. @acdlite noticed this didn’t fail the tests and suggested how to write one. i wrote one, and indeed, my code was still broken! you can see in last two commits how i fixed it and then hardened the test coverage for that bit.
anyway, that is just to say that writing code sometimes feels like detective work. first it is frustrating that you don’t understand how something works, but then you have a rough idea, then you have a flawed fix. at some point you just have the right fix and know how it works.
it is interesting to me how a failing test for one scenario has led to a change in a piece of code, which after a good review indicated insufficient coverage for a different scenario, leading to an extra test for that other scenario. fixing one bug hardened tests for other cases.
oh, and after the right fix? then you forget. that’s why you leave comments and PR descriptions behind.
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