TEST(QueryProjectionTest, IdExclusionProjectionPreservesOtherFields) {
    auto proj = createProjection("{}", "{_id: 0}");
    ASSERT_TRUE(proj.isFieldRetainedExactly("a"));
}
TEST(QueryProjectionTest, IdExclusionProjectionPreservesOtherFields) {
    auto proj = createProjection("{}", "{_id: 0}");
    ASSERT_TRUE(proj.isFieldRetainedExactly("a"));
}