Allow setting JSON_BuildTests=OFF from parent CMakeLists.txt

[FDUdannychen]

I think a standard BUILD_TESTING option is better in this case?

Meanwhile, setting JSON_BuildTests=ON prevents the user from disabling the unit test build from parent CMakeLists.txt.

[nlohmann]

What do you propose? Replacing JSON_BuildTests with BUILD_TESTING?

[FDUdannychen]

I want to disable building tests in my project's CMakeLists.txt. I have a thirdparty/CMakeLists.txt:

-myproj
    -src
        -CMakeLists.txt (build myproj sources)
    -thirdparty
        -json
        -another_lib
        -CMakeLists.txt (I want to disable json's unit tests here)

[nlohmann]

OK. I'm not a CMake expert. Could you describe what needs to be done or open a PR?

[FDUdannychen]

@nlohmann Sorry I just notice you are not using CTest. So BUILD_TESTING is not an option here. I'll pass -DBuildTests=OFF in a script instead of specify it in my CMakeLists.txt as a workaround. This issue should be closed.

[nlohmann]

In fact we are using ctest...

[theodelrieu]

I've seen quite a few cmake projects using BUILD_TESTS as an option. I thought it was an official option, apparently not.

IIUC, we're not including the CTest module, so the BUILD_TESTING option is missing?

[nlohmann]

Any ideas on this?

[TinyTinni]

I am not really sure, what the original issue is.
You can set JSON_BuildTests=OFF in your CMake script before including the json CMakeLIsts with e.g. add_subdirectory (don't forget declaring it as a CACHE variable, or using option instead of set).

IIUC, we're not including the CTest module, so the BUILD_TESTING option is missing?

Yes, regarding to the CTest doc, BUILD_TESTING is included when you include the CTest module via cmake (not done by the project atm).

The BUILD_TESTING seems to be a variable where you can control all tests of all projects included by cmake.

I would propose:

1. include CTest
2. add test targets only, when BUILD_TESTING and JSON_BuildTests are ON

This approach allows disabling all tests (of all parent/subprojects) with BUILD_TESTING or disabling just the json tests.

The problem would be in the existence of a single inconsistency:
When BUILD_TESTING is OFF, but JSON_BuildTests is ON.
Some people might think, the json tests will be build.

The default value of BUILD_TESTING is ON, so the approach described above is backward compatible.

ATM, I see no good approach that keeps backward compatibility and/or consistency of the 2 variables, when they get replaced and/or depends on each other.

Corresponding pull request: #885

[nlohmann]

Closed by merging #885.