Unity3D TestRunner hangs when using NSubstitute to mock a Monobehavior class - unit-testing

Question

I have stripped my project down to the bare minimum to try to figure out this instance where Unity TestRunner hangs. I have two Monobehaviors classes, GameController and TrialController. I followed Jason Wiemann's excellent testing videos Everything you need to know about Testing in Unity3D and Testing Against Monobehaviors Using Mocks to create an interface class, ITrialController, so that I can mock it for testing GameController. The TestRunner hangs when I try to run TestWithGetNextSubstitute(). What am I doing wrong here?
============== GameCtrlTest.cs ===========================
using System.Collections;
using System.Collections.Generic;
using NSubstitute;
using NUnit.Framework;
using UnityEngine;
using UnityEngine.TestTools;
namespace Tests
{
public class GameCtrlTest
{
GameController gameCtrl;
[SetUp]
public void TestSetup()
{
GameObject gameObject = new GameObject("GameController");
gameCtrl = gameObject.AddComponent<GameController>();
gameCtrl.trialCtrl = Substitute.For<ITrialController>();
Assert.IsNotNull(gameCtrl.trialCtrl);
Debug.Log("Test Setup() done");
}
[UnityTest]
public IEnumerator TestWithGetNextSubstitute()
{
gameCtrl.trialCtrl.GetNextTrial().Returns( "test-1", "test-2", null);
yield return null;
}
}
}
================== TrialController.cs ================================
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.Events;
public class TrialController : MonoBehaviour, ITrialController
{
int trialsLeft = 2;
public string GetNextTrial()
{
if (trialsLeft == 0)
return null;
else
{
string returnString = "trial--" + trialsLeft;
trialsLeft--;
return (returnString);
}
}
}
==================== ITrialController.cs =================
public interface ITrialController
{
string GetNextTrial();
}
==================== GameController.cs ==================
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
// give Test Runner access to internal variables and methods
[assembly: System.Runtime.CompilerServices.InternalsVisibleTo("Tests")]
public class GameController : MonoBehaviour
{
public ITrialController trialCtrl { get; set; }
//=================== MonoBehavior interface =======================
void Awake()
{
Debug.Log("gameController Awake()");
}
// Start is called before the first frame update
void Start()
{
Debug.Log("gameController Start()");
if (trialCtrl != null)
Debug.Log("trialCtrl already set");
else
{
Debug.Log("calling FindObjectOfType(typeof(TrialController)");
trialCtrl = (ITrialController)FindObjectOfType(typeof(TrialController));
Debug.Assert(trialCtrl != null, "Problem finding TrialController");
}
}
// Update is called once per frame
static bool levelInitialized = false;
void Update()
{
if (!levelInitialized)
{
Debug.Log("gameController first Update()");
levelInitialized = true;
}
string trialName = trialCtrl.GetNextTrial();
while (trialName != null)
{
Debug.Log($"GameController got {trialName} from GetNextTrial");
trialName = trialCtrl.GetNextTrial();
}
}
}

Answer 1

The fix was to move the GetNextTrial().Returns() call from the [UnityTest] to the [Setup]. This initially seems very limiting, but there is probably a way to move the parameter list ("test-1", "test-2", null) into a variable so I can change it for different tests.
=============== GameCtrlTest.cs ===================================
using System.Collections;
using System.Collections.Generic;
using NSubstitute;
using NUnit.Framework;
using UnityEngine;
using UnityEngine.TestTools;
namespace Tests
{
public class GameCtrlTest
{
GameController gameCtrl;
[SetUp]
public void TestSetup()
{
GameObject gameObject = new GameObject("GameController");
gameCtrl = gameObject.AddComponent<GameController>();
gameCtrl.trialCtrl = Substitute.For<ITrialController>();
Assert.IsNotNull(gameCtrl.trialCtrl);
gameCtrl.trialCtrl.GetNextTrial().Returns("test-1", "test-2", null);
Debug.Log("Test Setup() done");
}
[UnityTest]
public IEnumerator TestWithGetNextSubstitute()
{
yield return null;
}
}
}