bring in bugfix from #4532

DevProject/Assets/ML-Agents/Scripts/Tests/Runtime/AcademyTest/AcademyStepperTest.cs

@@ -0,0 +1,36 @@
+using System.Collections;
+using NUnit.Framework;
+using UnityEngine.TestTools;
+using UnityEngine;
+using UnityEngine.SceneManagement;
+using Unity.MLAgents;
+#if UNITY_EDITOR
+using UnityEditor.SceneManagement;
+#endif
+
+namespace Tests
+{
+    public class AcademyStepperTest
+    {
+        [SetUp]
+        public void Setup()
+        {
+            SceneManager.LoadScene("ML-Agents/Scripts/Tests/Runtime/AcademyTest/AcademyStepperTestScene");
+        }
+
+        /// <summary>
+        /// Verify in each update, the Academy is only stepped once.
+        /// </summary>
+        [UnityTest]
+        public IEnumerator AcademyStepperCleanupPasses()
+        {
+            var academy = Academy.Instance;
+            int initStepCount = academy.TotalStepCount;
+            for (var i = 0; i < 5; i++)
+            {
+                yield return new WaitForFixedUpdate();
+                Assert.True(academy.TotalStepCount - initStepCount == i + 1);
+            }
+        }
+    }
+}