public void ToString_UnsupportedKeyType()
        {
            var map = new MapField <byte, string> {
                { 10, "foo" }
            };

            Assert.Throws <ArgumentException>(() => map.ToString());
        }
        public void ToString_StringToString()
        {
            var map = new MapField <string, string> {
                { "foo", "bar" }, { "x", "y" }
            };

            Assert.AreEqual("{ \"foo\": \"bar\", \"x\": \"y\" }", map.ToString());
        }