cmake: Clean up testing code

[hebasto]

1. Delete CTest module.

The CTest module handles CDash integration, which we do not use. It is not required for testing functionality.

2. Clean up cases when to invoke enable_testing()

The enable_testing() command invocation is required for add_test() commands, which are used only for {noverify_}tests, exhaustive_tests and examples.

[real-or-random]

The enable_testing() command invocation is required for add_test() commands, which are used only for {noverify_}tests, exhaustive_tests and examples.

I don't think it's required. It's just that add_test() has no effect without enable_testing().

enable_testing() seems cheap. Couldn't we just run it always? Or do you think this has drawbacks?

[hebasto]

The enable_testing() command invocation is required for add_test() commands, which are used only for {noverify_}tests, exhaustive_tests and examples.

I don't think it's required. It's just that add_test() has no effect without enable_testing().

enable_testing() seems cheap.

I agree.

Couldn't we just run it always?

Sure. The code has been adjusted.

Or do you think this has drawbacks?

I did some research and I haven't found any drawbacks. When enable_testing() is invoked and no tests being added, the created CTestTestfile.cmake files in the binary tree are noop/empty.

It is recommended:

to call enable_testing() somewhere in the top level CMakeLists.txt file. This would typically be done early, soon after the first project() call.

[real-or-random]

utACK 7c987ec

[theStack]

ACK 7c987ec

I don't have too much knowledge about CMake, but following the discussion here and reading some CMake forum discussions (e.g. https://discourse.cmake.org/t/is-there-any-reason-to-prefer-include-ctest-or-enable-testing-over-the-other/1905/2), the simplification looks correct.

I did some research and I haven't found any drawbacks. When enable_testing() is invoked and no tests being added, the created CTestTestfile.cmake files in the binary tree are noop/empty.

Verified this by creating a fresh build directory via

$ rm -rf ./build && cmake -B build -DSECP256K1_BUILD_BENCHMARK=OFF -DSECP256K1_BUILD_TESTS=OFF -DSECP256K1_BUILD_EXHAUSTIVE_TESTS=OFF -DSECP256K1_BUILD_CTIME_TESTS=OFF
$ cat ./build/src/CTestTestfile.cmake

and checking that the file only contains comment. If one of these options is ON, the file contains add_test(...) calls.