Fix off-by-one error on AgentReset and maxSteps (#3394)

* Fix ballance ball 100 reward

* Re-test

* Add test for maxSteps and number of AgentActions

Co-authored-by: Chris Elion <celion@gmail.com>

com.unity.ml-agents/Runtime/Agent.cs

         /// Used by the brain to make the agent perform a step.
         void AgentStep()
         {
-            if ((m_StepCount >= maxStep - 1) && (maxStep > 0))
+            if ((m_StepCount >= maxStep) && (maxStep > 0))
             {
                 NotifyAgentDone(true);
                 _AgentReset();
                 m_StepCount += 1;
             }
+
             if ((m_RequestAction) && (m_Brain != null))
             {
                 m_RequestAction = false;

com.unity.ml-agents/Tests/Editor/MLAgentsEditModeTest.cs

 
         public int initializeAgentCalls;
         public int collectObservationsCalls;
+        public int collectObservationsCallsSinceLastReset;
+        public int agentActionCallsSinceLastReset;
         public int agentResetCalls;
         public override void InitializeAgent()
         {
         public override void CollectObservations()
         {
             collectObservationsCalls += 1;
+            collectObservationsCallsSinceLastReset += 1;
             AddVectorObs(0f);
         }
 
+            agentActionCallsSinceLastReset += 1;
             AddReward(0.1f);
         }
 
+            collectObservationsCallsSinceLastReset = 0;
+            agentActionCallsSinceLastReset = 0;
         }
 
         public override float[] Heuristic()
             var j = 0;
             for (var i = 0; i < 500; i++)
             {
-                if (i % 20 == 0)
+                if (i % 21 == 0)
                 {
                     j = 0;
                 }
 
                 agent1.AddReward(10f);
                 aca.EnvironmentStep();
+            }
+        }
+
+        [Test]
+        public void TestMaxStepsReset()
+        {
+            var agentGo1 = new GameObject("TestAgent");
+            agentGo1.AddComponent<TestAgent>();
+            var agent1 = agentGo1.GetComponent<TestAgent>();
+            var aca = Academy.Instance;
+
+            var decisionRequester = agent1.gameObject.AddComponent<DecisionRequester>();
+            decisionRequester.DecisionPeriod = 1;
+            decisionRequester.Awake();
+
+            var maxStep = 6;
+            agent1.maxStep = maxStep;
+            agent1.LazyInitialize();
+
+            for (var i = 0; i < 15; i++)
+            {
+                // We expect resets to occur when there are maxSteps actions since the last reset (and on the first step)
+                var expectReset = agent1.agentActionCallsSinceLastReset == maxStep || (i == 0);
+                var previousNumResets = agent1.agentResetCalls;
+
+                aca.EnvironmentStep();
+
+                if (expectReset)
+                {
+                    Assert.AreEqual(previousNumResets + 1, agent1.agentResetCalls);
+                }
+                else
+                {
+                    Assert.AreEqual(previousNumResets, agent1.agentResetCalls);
+                }
             }
         }
     }