Boost CMake testing procedure doesn't work for StaticString

[pdimov]

The documented testing procedure

mkdir __build && cd __build
cmake -DBUILD_TESTING=ON -DBOOST_INCLUDE_LIBRARIES=static_string ..
cmake --build . --target tests
ctest --output-on-failure --no-tests=error

fails for Boost.StaticString, because the test executables aren't built by the target tests. BoostTest handles this automatically, but for tests declared manually, one needs to first declare the tests target if not present

if(NOT TARGET tests)
    add_custom_target(tests)
endif()

and then for each test executable, use add_dependencies(test my_test_executable).

Or, since there is already a target boost_static_string_all_tests, it should be enough to make it a dependency of tests: add_dependencies(tests boost_static_string_all_tests).

(For this to keep working after the eventual fix, it might be a good idea to add it to CI.)

It's also good practice to make the test executables EXCLUDE_FOR_ALL, so that building the tests target builds them, but building the default target doesn't, but this step is not in principle required.

[pdimov]

Is this going to be fixed? It breaks the tests of Mysql.

[sdkrystian]

@pdimov Looking into it

[alandefreitas]

Probably this one fixes it: #54