cmake --build . --target all instead of specific target

Lets assume I cloned a big project with lots of libraries.

The dependency graph is complex. 
I want to run the unit tests of a library that many other libraries in this project depend on.

• The step `cmake ..\build_dir` is done.
• I would choose the test executable in the RUN menu and hit run.

My expectation would be:
qtcreator executes

cmake --build . --target test_executable_name

to build only this test executable and its dependencies.

But instead qtcreator runs

cmake --build . --target all

And builds the whole project, which takes an hour or more  instead of a few seconds for the specific test executable.