Karma-coverage infers the instrumenter regarding of the file extension. The `.coffee` files are by default covered using [Ibrik](https://github.com/Constellation/ibrik) (an [Istanbul](https://github.com/gotwarlost/istanbul) analog for CoffeeScript files). It is possible to override this behavior and point out an instrumenter for the files matching a specific pattern. To do so, you need to declare an object under with the keys representing the pattern to match, and the instrumenter to apply. The matching will be done using [minimatch](https://github.com/isaacs/minimatch). If two patterns match, the last one will take the precedence.