spock mocking getting error TooFewInvocationsError when testing a call on an injected object

I am trying to test a call to another object instance method. I have injected the User object into the Chitter class and stored the new object in a variable. The methods login(name) and logOut(name) calls the object's method, injected into chitter class. The Object, users, is a separate class and is tested, so the methods 'loginUser(name)' and 'logOutUser()' are working.

I have tried using the following to test that when login(name) is called, it calls the loginUser(name) once. But I am getting the following error message:

Too few invocations for:

1 * usersSignedUp.loginUser("Spike")   (0 invocations)

Unmatched invocations (ordered by similarity):

None


at org.spockframework.mock.runtime.InteractionScope.verifyInteractions(InteractionScope.java:78)
at org.spockframework.mock.runtime.MockController.leaveScope(MockController.java:76)
at ChitterSpec.Chitter can login a user(ChitterSpec.groovy:24)

I get the same message for the logout() method too.

I assume I am using mocks the wrong way. But I did the same thing in another project and it worked, although I did not create the other object when I instantiated the object.

How do I get this test pass

Here is the code:

//Chitter.groovy

class Chitter {
  private def usersSignedUp

  def Chitter(users = new Users()){
    usersSignedUp = users
  }

  def getActiveUser(){
    usersSignedUp.getLoggedInUser()
  }

  def getUsersSignedUp(){
    this.usersSignedUp
  }
  //These are the methods the tests are failing for
  def login(name) {
   usersSignedUp.loginUser(name)
  }

  def logOut() {
    usersSignedUp.logOutUser()
  }
}

For the tests (using spock and gradle)

//ChitterSpec.groovy
import spock.lang.*

class ChitterSpec extends Specification {
  def chitter
  Users users

  def setup() {
        users = GroovySpy()
        chitter = new Chitter()
  }

  def 'no user has logged in at start'() {
        expect:
        chitter.getActiveUser() == null
  }

  def 'no users stored at the start'() {
        expect:
        chitter.getUsersSignedUp().getListofUsers() == []
  }
  //Failing tests below
  def 'Chitter can login a user'() {
        when:
        chitter.login('Spike')

        then:
        1 * users.loginUser("Spike")
  }

  def 'Chitter can logout a user'() {
        when:
        chitter.logOut()

        then:
        1 * users.logOutUser()
  }
}

The rest of my code can be seen here http://ift.tt/2alJtSS