System Test Java

gistfile1.java

public class System {
        public System(Authorizer authorizer) {
                this.authorizer = authorizer;
        }

        public int loginCount() {
                //returns number of logged in users.
        }
}

@Test
public void newlyCreatedSystem_hasNoLoggedInUsers() {
        System system = new System(new DummyAuthorizer());
        assertThat(system.loginCount(), is(0));
}