How can i create this data structer?

I wanna write the data structure that will run the following function But i have questions.

`func TestDependsAA(t *testing.T) {
    s := NewRuleSet()  //IS THIS CLOSURE?
    s.AddDep("a", "a") //If that is a closure, What is this?
    if !s.IsCoherent() {
        t.Error("s.IsCoherent failed")
    }
}`