Though I did manage to crash the Canvas 3D extension by feeding it a negative vertex attribute id as it was using it to do some cache array indexing (int id, only checked for
id >= arrayLength.) Got a hacky copy-pasted-from-Context2D.cpp SOP checking going and passing tests for it. Trying to #include "nsHTMLVideoElement.cpp" duly broke the build, so no video element texImage2DHTML.
Remaining things in my shortlist of tests to write are: vertexAttribPointer, vertexAttrib, uniform[fi], bufferData, bufferSubData. Then it's time for secondary tests (methods that have custom implementations and especially getters and things that take indices.)
My testing priority heuristic goes something like this: Deals with web data => SOP bugs. Array indexing => segfaults. Segfaults => you're pwned, dood. State => bugs. Allocation => memleaks. New code => new bugs. Complex logic => complex bugs. No code => maybe no bugs, who knows.
So code I like pushes everything through well-trodden paths with the least amount of new code and in the simplest way possible. Preferably without array indexing, heap allocation, or state of any kind.