Simple example of colcon test

edit

I am just starting to use ROS2. I have built a talker and a listener.

I also have a much more complex project that I have to understand.

so far I have understood about colcon build, but I would really appreciate if someone can point me to a simple way to use colcon test.

What is the general procedure if say I write a talker and listener in C++ and want to do some testing? Do my test have to be written in C++? or python?

I believe the way to understand complex things is to start simple so I would appreciate some help here. Later perhaps I could ask more specific questions.