Unit test for int key dictionaries

Topten.JsonKit.Test/TestDictionary.cs

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+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Topten.JsonKit;
+using Xunit;
+
+namespace TestCases
+{
+    public class TestDictionary
+    {
+        [Fact]
+        public void DictionaryNonStringKeys()
+        {
+            var dict = new Dictionary<int, double>()
+            {
+                [-1] = 50,
+                [0] = 100,
+                [1] = 200,
+            };
+
+            var json = Json.Format(dict);
+
+            var dict2 = Json.Parse<Dictionary<int, double>>(json);
+
+            Assert.Equal(dict, dict2);
+        }
+    }
+}