        Please help me generate a whole C++ unit test for a focal method in a focal class. I will provide the following information:
            1. Required dependencies to import.
            2. The focal class signature.
            3. Source code of the focal method.
            4. Signatures of other methods and fields in the class.
            I need you to create a whole unit test using GoogleTest and C++, ensuring optimal branch and line coverage.
            The test should include necessary imports for GoogleTest, compile without errors.No additional explanations required.
            Only Code is needed.
            The focalmethod is sub in focal class Calc. The method:
            int Calc::sub(int a, int b) {
    return a-b;
}
            The imports:  b'#include "calc/Calc.h"\n'
            Other methods and fields:  add
            Code: Write your response with at least 700 words.
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