Disable Estimator tests if BUILD_UNIT_TESTS is set to OFF.

[stephan-rohr]

Please review the developer documentation
on the wiki of this project that contains help and requirements.

Proposed changes

The 'test_estimators' binary is build independent of the setting of BUILD_UNIT_TESTS. This causes a linker error as 'sposets_for_testing' library is not available. Disable tests for Estimators if BUILD_UNIT_TESTS is OFF.

What type(s) of changes does this code introduce?

• Build related changes

Does this introduce a breaking change?

• No

What systems has this change been tested on?

Checklist

• Yes. This PR is up to date with current the current state of 'develop'
• No. Code added or changed in the PR has been clang-formatted
• No. This PR adds tests to cover any new code, or to catch a bug that is being fixed
• No. Documentation has been added (if appropriate)

[prckent]

Thanks Stephan.

Looks good to me. I think this was not caught before since it is a rarely used config option.

[prckent]

Test this please

[ye-luo]

On which OS system and with what compiler , the linking failed?

[stephan-rohr]

On which OS system and with what compiler , the linking failed?

It failed on ubuntu-20 with intel oneAPI 2023.2.0 compiler.