[C++] Provide option to opt out of installing tests

[h-vetinari]

Describe the enhancement requested

Since conda-forge/arrow-cpp-feedstock#1058, we have unintentionally been shipping the following in libarrow-all

lib/cmake/ArrowFlightTesting/ArrowFlightTestingConfig.cmake
lib/cmake/ArrowFlightTesting/ArrowFlightTestingConfigVersion.cmake
lib/cmake/ArrowFlightTesting/ArrowFlightTestingTargets-release.cmake
lib/cmake/ArrowFlightTesting/ArrowFlightTestingTargets.cmake
lib/cmake/ArrowTesting/ArrowTestingConfig.cmake
lib/cmake/ArrowTesting/ArrowTestingConfigVersion.cmake
lib/cmake/ArrowTesting/ArrowTestingTargets-release.cmake
lib/cmake/ArrowTesting/ArrowTestingTargets.cmake
lib/cmake/ArrowTesting/FindGTestAlt.cmake
lib/libarrow_flight_testing.so
lib/libarrow_flight_testing.so.1801
lib/libarrow_flight_testing.so.1801.0.0
lib/libarrow_testing.so
lib/libarrow_testing.so.1801
lib/libarrow_testing.so.1801.0.0
lib/pkgconfig/arrow-flight-testing.pc
lib/pkgconfig/arrow-testing.pc

I didn't check this more closely because my experience with other CMake projects is that tests don't get installed by default (but need a specific opt-in). It would be nice to have an ARROW_INSTALL_TESTS to go along with ARROW_BUILD_TESTS which controls whether these files get installed.

I care less about the choice of default for ARROW_INSTALL_TESTS (or whatever it ends up being called), though I think it should be set to False.

Component(s)

C++, Packaging

[kou]

libarrow_testing and libarrow_flight_testing are not tests. They are utility libraries to write tests.

It's better that conda creates separated subpackages for them. For example, libarrow-testing for libarrow_testing and libarrow-flight-testing for libarrow_flight_testing.

[h-vetinari]

libarrow_testing and libarrow_flight_testing are not tests. They are utility libraries to write tests.

OK, they're test infrastructure.

It's better that conda creates separated subpackages for them.

I'm not interested in shipping these things unless a very concrete use-case comes up, otherwise we're just wasting everyone's bandwidth and storage for nothing.

I only want to test the library, and then not install the tests and any test-only infrastructure. I can do this manually, but that's fragile if arrow ever adds new stuff that ends up getting installed through ARROW_BUILD_TESTS. It should not be controversial to separate building tests (+ whatever else comes along!) from installing them?

[xhochy]

They are utility libraries to write tests.

This means though that:

1. Other packages could use them.
2. They should be always built, not only when testing is turned on.

Right?