What kind of tests can be written for the function?

Trying to come up with Karma tests for AngularJS service, but facing some difficulties. Dont know what tests exactly to write. Could anyone help? For example, what should i write for the follwong function:

authorization() {
    let t = this;
    var authorized = Boolean(localStorage.getItem('authorized'));
    var memorizedState = null;
    var
      clear = function () {
        localStorage.removeItem('authorized');
        localStorage.removeItem('currentUser');
        authorized = false;
        memorizedState = null;
        t.$state.go('auth');
      },
      go = function (fallback) {
        localStorage.setItem('authorized', 'true');
        authorized = true;
        var currentUser = localStorage.getItem('currentUser');
        var targetState = memorizedState ? memorizedState : fallback;
        t.$state.go(targetState);
      };
    return {
      authorized: authorized,
      memorizedState: memorizedState,
      clear: clear,
      go: go
    };
  }