[aianus]

Not exactly a fair comparison, because you have to compile the changed files first and link which I'm sure takes longer than 14s.

On the other hand, using ruby I can have it continuously run the tests for the specific feature I'm working on without the long building step.

[Ono-Sendai]

Compiling a changed file and linking takes about 5s.

[mappu]

Is that the best case for changing a single cpp file, or the worst case for changing a header file shared across many translation units?

[Ono-Sendai]

That's changing a cpp file. Changing a widely used header file could take 1-2 mins for a full or nearly full rebuild.