another main.cpp inside test directory

I will start writing my first unit tests for a project soon, and I plan on storing them in a directory called test. Inside this directory, I have been advised to have another main.cpp file, in addition to other main.cpp in my src directory.

Does the compiler build two executables or something? How can you run this test inside an IDE? I am using codelite, which appears to have some support for UnitTest++, but I plan on using Boost Test.