I don't think this is a good idea. Calling a command from another one is not the clean way to reuse the logic (especially if the seond command is not meant to be public, as it makes no sense to have it as a command).
If you need to share logic between commands, the clean way is to extract this logic in a service used by both commands

Ok, fair enough. I've never used calling a command from a command myself, but though some people might want to use it. But there are indeed better ways of reusing code. I will remove the comment and override add() to throw an exception.

Why did you change the argument type?

Because InSingleCommandApplicationTest::testRun() I use it, providing it with anArgvInput instance instead of an array.
Otherwise I can not properly test the real command line interface handling.

Allowing$input to be anInputInterface makesApplicationTester::run() more flexible and useful as test helper imho.

I fail to see a difference in using ArrayInput vs ArgvInput in the application tester. What am I missing? It's not a job of the application tester to test cli handling.

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 anInputInterface object, instead of a less flexible array.

It's not a job of the application tester to test cli handling.

True, but forSingleCommandApplicationTest 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 useArrayInput instead ofArgvInput, but ended up finding out that ArrayInput does not properly support input arguments of typeIS_ARRAY, around which a large part of theSingleCommandApplication tests are written. So, I'm not sure if usingArrayInput instead of the currentArgvInput is the best option at the moment.

I think for an ApplicationTester this change is ok, if not then i don't see a problem splitting and having a SingleApplicationTester if it makes it simpler to test, no? although this is a small change for creating a new class. Could you not rather adapt your tests to comply with theArgvInput?

Unfortunately, removing the type hint would be a BC break.

Ok, I'll drop usage of ApplicationTester and roll my own alternatuve (apparently just takes about 6 LOC for the functionality I need)

FYI: I dropped usage ofSymfony\Component\Console\Tester\ApplicationTester and the removal of the array type hint inApplicationTester::run(array $input, $options)
(which apparently broke BC) and replaced it with the low fat roll-your-own alternative above