Make process runner configurable

[hugo-vrijswijk]

Fixes #36

Added the option to configure the test command that the ProcessRunner runs. It can be configured with a command-runner test-runner. Future test-runners could be configured in a way similar to Stryker's test-runners and read in the TestReader.

I added a new TestRunner config value instead of adding the correct MutantRunner as it made more sense to me to keep configuration in the Config object instead of adding an implementation to it. I am not sure about the naming of the classes yet, I think they are confusing. But also don't know what would be better.

[legopiraat]

Somehow I feel icky about the command because if the user defines the full command we will not be able to preserve the session for example sbt which we would like to do. I think I would be more of a fan to split of the process runner command from the other command, something like:

{
    command-runner: {
          runner: "sbt"
          command: "test -DskipStuff=true"
     }
 }

For sure this will make it usable for all build tools but it has some big downsides.

[nicojs]

Great that you're using the same name here: command-runner is also the name Stryker uses

[hugo-vrijswijk]

@legopiraat I imagine with a SBT (or other) plugin the syntax would be like this, as it won't be a command-runner:

test-runner: "sbt"

I'm not opposed to splitting the command and args into separate values. That would also make it easier to put out a warning when we have a plugin to use instead.

[legopiraat]

If you don't mind I think it would be a good idea to split it up. And indeed it will be easier for us to putt out the notifications I suppose a lot of users would appreciate that.

[hugo-vrijswijk]

I've split the command and args into separate values

[legopiraat]

Why the custom ConfigReader, maintainability is not that good. To get better maintainability we could and should make it an ADT and use option one.

https://pureconfig.github.io/docs/complex-types.html

[legopiraat]

Let's make an issue for these toString methods, it's already getting tedious in my opinion.

We should be able to generate this format really easy I guess.

[legopiraat]

Should be private

[hugo-vrijswijk]

Turns out Pureconfig also has a ConfigWriter function, for writing objects to Typesafe config. I've implemented this, which also fixes #39. I've also removed the TestRunnerReader completely, though the configuration is slightly different. Configuring the TestRunner would now look like this:

test-runner: {
  type=commandrunner
  command: "mvn"
  args: "clean test" 
}

I'm not completely opposed to the type argument, as I think it's still clear what the option does.