Allow inserting source files in the HEAD / custom context.html

Based on #430

Let’s allow custom context.html and debug.html.

Add two config options:

• contextFile (default __dirname + ‘…/static/context.html’)
• debugContextFile (default __dirname + ‘…/static/debug.html’)

[dignifiedquire]

Done in #1825

[rosenfeld]

I believe there are many reasons why allowing custom HTML would be desirable. It gives other projects flexibility to do basically any kind of experimentation with Karma without having to fork the project.

In our specific case, we use oojspec to run unit and integration tests with a single runner. Most integration test runners out there are pretty slow, like Capybara, Selenium or anything using a real browser, headless like phantomjs or not.

OOJSpec doesn’t enforce the way people should write code. If someone wants to be able to register events on DOM selectors which are never unregistered because it’s not needed in the application, they shouldn’t change the way they write their code just to satisfy their test runner limitations. So, one is free to register those events once in a beforeAll block and then run a set of tests, which may depend or not on previous tests (they are always run in the specified order by specification) which allows some integration scenarios to be tested more quickly than it would be if the tests had to be written in an independent way and also gives developers more flexibility on how they write code.

For this to work, OOJSpec has to run each set of tests, grouped in an specification file, in a separate iframe. OOJSpec currently uses sprockets to create such structure in a similar way adopted by other gems like Konacha and others. It would be awesome to be able to use Karma infra-structure to run a custom HTML runner created to be compatible with Karma API so that it reports the tests run correctly to the client console. It should be doable once we have the ability to specify how the HTML should be written. My plan is to integrate OOJSpec to webpack and test with Karma and stop using sprockets. Another advantage of running the tests in separate iframes is that you are able to test whether all required dependencies were correctly declared since only the dependencies for that test file are loaded in the isolated iframe.