[C++] Add support for building arrow_testing without building tests

[asfimport]

ARROW_BUILD_TESTS installs the following arrow_testing related files implicitly:

lib/cmake/arrow/ArrowTestingConfig.cmake
lib/cmake/arrow/ArrowTestingConfigVersion.cmake
lib/cmake/arrow/ArrowTestingTargets-%%CMAKE_BUILD_TYPE%%.cmake
lib/cmake/arrow/ArrowTestingTargets.cmake
lib/cmake/arrow/FindArrowTesting.cmake
lib/libarrow_testing.so
lib/libarrow_testing.so.100
lib/libarrow_testing.so.100.1.0
libdata/pkgconfig/arrow-testing.pc

If we have ARROW_TESTING or something, users can do it explicitly.

The original GitHub bug report: #8306

Reporter: Yuri / @yurivict
Assignee: Kouhei Sutou / @kou

PRs and other links:

• GitHub Pull Request #8356

_{Note: This issue was originally created as ARROW-10139. Please see the migration documentation for further details.}

[asfimport]

Kouhei Sutou / @kou:
I think that libarrow_testing.so is an useful library to write tests for 3rd party libraries.
Especially, arrow::random::RandomArrayGenerator is useful to create test data.

[asfimport]

Yuri / @yurivict:
Then it would make sense to split the current ARROW_BUILD_TESTS into 2 options: (1) build tests for local testing, and (2) install files for third party test libraries.

 

[asfimport]

Kouhei Sutou / @kou:
BTW, what is the problem of installing these files?
Packaging?

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Yuri / @yurivict:
Because the explanation of the cmake option doesn't lead one to believe that any files need to be installed.

In order to test the project one doesn't need to install any extra files.

[asfimport]

Kouhei Sutou / @kou:
OK.

How about adding new ARROW_TESTING option like existing ARROW_${COMPONENT} options and changing ARROW_BUILD_TESTS to enable ARROW_TESTING implicitly?
If ARROW_TESTING is enabled, libarrow_testing.so is built and installed.
If ARROW_BUILD_TESTS is enabled, ARROW_TESTING is enabled implicitly. So libarrow_testing.so is installed by ARROW_BUILD_TESTS.

[asfimport]

Yuri / @yurivict:
That would work.

[asfimport]

Kouhei Sutou / @kou:
Issue resolved by pull request 8356
#8356