How to get size of struct containing data structures in Go?

I'm currently trying to get the size of a complex struct in Go.

I've read solutions that use reflect and unsafe, but neither of these help with structs that contain arrays or maps (or any other field that's a pointer to an underlying data structure).

Example:

type testStruct struct {
    A     int
    B     string
    C     struct{}
    items map[string]string
}

How would I find out the correct byte size of the above if items contains a few values in it?