doctest/examples/executable_dll_and_plugin/implementation.cpp

#define DOCTEST_CONFIG_IMPLEMENTATION_IN_DLL
#define DOCTEST_CONFIG_IMPLEMENT
#include <doctest/doctest.h>

DOCTEST_MAKE_STD_HEADERS_CLEAN_FROM_WARNINGS_ON_WALL_BEGIN
#include <iostream>
DOCTEST_MAKE_STD_HEADERS_CLEAN_FROM_WARNINGS_ON_WALL_END

TEST_CASE("implementation") {
    std::cout << "I am a test from the implementation!" << std::endl;
}