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This is an interesting and possibly overlooked problem with using slow languages like Ruby - your unit tests take forever to run. (unless you spend a lot of engineering effort on making them run faster, in which case they may run somewhat acceptably fast)

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This isn't just a problem with Ruby. Our ObjC test suite for a project I work on takes about 10 min to run, too.

Our main product has approximately 5400 unit tests, over ~150 files. The test suite runs on a single computer in about 14s. This is one of the advantages of using a fast language (C++) with multithreading :)

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.

Compiling a changed file and linking takes about 5s.

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?

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

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