Add some component tests to reference unity project (#86)

* Add some component tests to reference unity project

* Use action/setup-node@v2 to avoid problems with build

unity-project-with-correct-tests/Assets/Tests/PlayMode/SampleComponentTest.cs

@@ -0,0 +1,31 @@
+using System.Collections;
+using NUnit.Framework;
+using UnityEngine;
+using UnityEngine.TestTools;
+
+namespace Tests
+{
+  public class SampleComponentTest
+  {
+    private GameObject target;
+    private SampleComponent component;
+
+    [SetUp]
+    public void Setup()
+    {
+      target = GameObject.Instantiate(new GameObject());
+      component = target.AddComponent<SampleComponent>();
+    }
+
+    [UnityTest]
+    public IEnumerator TestIncrementOnUpdateAfterNextFrame()
+    {
+      // Save the current value, since it was updated after component Start() method called
+      var count = component.Counter.Count;
+
+      // Skip frame and assert the new value
+      yield return null;
+      Assert.AreEqual(count + 1, component.Counter.Count);
+    }
+  }
+}