Add note on running tests in parallel

Author: uekerman

05_testing_and_ci/boost_testing_precice_demo.md

@@ -49,3 +49,7 @@ Look around preCICE in the terminal + text editor.
 ## CMake
 
 - Look at `cmake/CTestConfig.cmake`: Complicated, but more things tested than only UTF (search for `add_test`)
+
+## CTest in Parallel
+
+- Build preCICE and run tests via `ctest -j 16`, runs tests in parallel, automatic feature of CTest

05_testing_and_ci/boost_testing_sidemade_demo.md

@@ -50,6 +50,8 @@ Repository: [testing boost exercise – demo-start branch](https://github.com/Si
     target_link_libraries(testsidemade PRIVATE Boost::unit_test_framework)
     add_test(NAME "MatrixSolverTests" COMMAND ${CMAKE_CURRENT_BINARY_DIR}/testsidemade)
     ```
+    
+    - `add_test` can work with anything that returns an exit code. Does not have to be a fancy testing framework.
 
 - Reconfigure CMake, build, run via ...
     - `./testsidemade`