Easily debug initial test run

[nicojs]

We need a way to debug the initial test run more easily. Right now its a pain.

Take this workflow for example:

1. Rerun stryker using logLevel: 'trace'
2. Lookup the karma config it prints to the console
3. Shut down Stryker
4. Move the karma config to a seperate karma.conf.js file
5. Change reporters to include the 'progress' reporter.
6. Run karma on the newly created config. Interpret what the issue is. Fix and rerun.
7. Alter stryker.conf.js and start again from 1.

Once we have this feature: #171 we could add a debug command for example.

The debug command should:

1. Print log messages from the test runner.
2. Give the user the possibility to inspect the test runner (the browser if you're using karma).

In order for 1 to work, we should run the testrunner in the same process as Stryker. No isolation into a separate process.

In order for 2 to work, we should notify the test runner that it is ran with the debug command (command: 'debug' or something). The stryker-karma-runner could than load the test run with singleRun: false` for example, keeping the browser open.

@sharikovvladislav what do you think of this proposal? Would this be helpful enough for you?

[sharikovvladislav]

I can debug unit tests which are using karma runner in IDEA/WebStorm (like any other nodejs/grunt/gulp/etc application). I just put breakpoint in code, run debug and . Will I be able to do it after this implementing this feature?

[nicojs]

Ah yes, you probably will. It will be the same process as Stryker runs in, so running stryker with the debugger might just do the trick. Not sure though, we'll have to see.

[simondel]

@nicojs Stryker will now suggest rerunning when it fails unexpectedly. Can we close this?

[nicojs]

It might we worth it to introduce a --runInBand flag (like jest's --runInBand).

If anyone wants this feature, please comment here, so we can reopen it.