I think you should move to the model I propose above.

In integration_test.h declare

namespace mongo {
namespace unittest {

struct IntegrationTestParams {
// ... 
};

extern IntegrationTestParams integrationTestParams;

} // namespace unittest
} // namespace mongo

And then create a integration_test.cpp file that declares the global:

namespace mongo {
namespace unittest {

IntegrationTestParams integrationTestParams;

} // namespace unittest
} // namespace mongo

Then, any file that includes integration_test.h can access integrationTestParams.