This bug will be tackled in smaller chunks, in the following order: 1. first batch of tests will focus on correctly computing transforms in calculateDrawTransformsAndVisibility. 2. second batch of tests will focus on verifying that the appropriate render surfaces and layer lists are created. 3. third batch of tests should make sure scissor rects and drawableContent rects are being computed correctly. 4. additional tests for any important special cases, and for other functions in this class. 5. with tests in place, it will be appropriate to consider refactoring this to make it more intuitive and less error-prone. - const where possible - separating chunks of code into helper functions I am already working on Step 1, which is a dependency on other work that we want to land soon.
Looks like we've come a long way for this, and this bug is somewhat obsolete. There are now more than 50 tests for this code. Thanks to everyone who's been dutifully adding unit tests!!! Ideally we will still need a bit more rigorous coverage of a few more hidden corners, but I think its quite reasonable to close this bug now, for our bookkeeping.