Add tests for PlayMode and EditMode

sample-project/Assets/Scripts/BasicCounter.cs

@@ -0,0 +1,18 @@
+using System;
+
+public class BasicCounter
+{
+  public const int MaxCount = 10;
+
+  public BasicCounter(int count = 0)
+  {
+    Count = count;
+  }
+
+  public void Increment()
+  {
+    Count = Math.Min(MaxCount, Count + 1);
+  }
+
+  public int Count { get; private set; }
+}