If you are used to the latest versions of MS Visual Studio, then you should free up space on your desk and mark it with a giant "X" - this is inevitable when your fist and maybe even your head will be disappointed when using eclipse / CDT.
Eclipse has its own dependency mechanism, which does almost nothing, but, fortunately, the CDT module has its own dependency mechanism, which tries to do what you want. To configure project dependencies:
Project-->Properties-->C/C++ General-->Paths and Symbols-->References
So, in your example, you will go to the project properties for "libxxx_tests" and select "libxxx.a" as the dependency.
Please note that you can also use this page to set the order of libraries, which can be an important step depending on the complexity of your project.
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