feat(config): instrumenter override option

[gvarsanyi]

(As a result of PR-77 conversations)

Enable fine-tuning which preprocessor should be used for which files.
Add README.md section
Add test, update existing tests to comply with new dependency requirement

[aymericbeaumet]

I would say:

Force the use of the Istanbul instrumenter to cover CoffeeScript files

[aymericbeaumet]

Good work.

One last thing to note: in order to avoid the initialization of a useless instrumenter, I would defer its loading (i.e. Istanbul/Ibrik loading) after the for loop used to determined which instrumenter should be used, and so only load the appropriate one. It's a small optimization, but since you're at it.

[gvarsanyi]

Thank you.
I have updated the code and the readme file as per your request (with the exception of the process.exit(1) one, see my concern described in the line note conversation above).

[aymericbeaumet]

I'll answer here as this diff is now outdated (and so hidden).

I totally agree with you, the use of return process.exit(1); would have been incorrect as we don't have the right to exit the process at this place. Thanks for noticing it.

A callback 'done' is passed to the function where the error could occur. You should be able to do what you want by calling it with the desired exit code.

[gvarsanyi]

After some research now I think I get the idea behind done(). Still find it weird that one can't pass an actual error object/msg there, but alas: it does not break the async principals.

Updated the code to do the error handling now. Also moved out the check from the per-file cycle. Other then the smaller performance benefit it is needed to avoid having multiple error messages for the same error.

Thanks for the help, appreciate it.

[aymericbeaumet]

Did you tried to pass an unknown instrumenter? Was the error code correctly forwarded to the karma.server.start callback?

[gvarsanyi]

yes, I have tried, it comes back with exit_code === 1 for sthg like this if a bugous instrumenter name is passed in (0 otherwise).

karma = require 'karma'
karma.server.start options, (exit_code) ->
  console.error('Exit code:', exit_code) if exit_code > 0

[aymericbeaumet]

Ok nice, could you please add a test case for it?

[gvarsanyi]

Added

[aymericbeaumet]

Correct the commit message and I'll merge it.

[gvarsanyi]

hm, somehow the first line got lost in squashing. Fixed.