Separate test cases across multiple files in google test

Create one file that contains just the main to run the tests.

// AllTests.cpp
#include "gtest/gtest.h"

int main(int argc, char **argv)
{
    testing::InitGoogleTest(&argc, argv);
    return RUN_ALL_TESTS();
}

Then put the tests into other files. You can put as many tests as you like in a file. Creating one file per class or per source file can work well.

// SubtractTest.cpp
#include "subtract.h"
#include "gtest/gtest.h"

TEST(SubtractTest, SubtractTwoNumbers)
{
    EXPECT_EQ(5, subtract(6, 1));
}

This does require that all tests can share the same main. If you have to do something special there, you will have to have multiple build targets.