I fail to see a difference in using ArrayInput vs ArgvInput in the application tester
That's a bit my point: `ApplicatationTester` can be made agnostic about this and just accept an `InputInterface` object, instead of a less flexible array.

    It's not a job of the application tester to test cli handling.
True, but for `SingleCommandApplicationTest` it doesn't hurt that there is additional testing of the cli handling, which is slightly different than "traditional" applications (no first "command" argument).

Anyway, I tried to change my patch to use `ArrayInput` instead of `ArgvInput`, but ended up finding out that ArrayInput does not properly support input arguments of type `IS_ARRAY`, around which a large part of the `SingleCommandApplication` tests are written. So, I'm not sure if using `ArrayInput` instead of the current `ArgvInput` is the best option at the moment.