public void SetUp()
        {
            _dictionary = new StringStringDictionary();
            _readOnly   = _dictionary.AsReadOnly();
            Assert.AreEqual(0, _dictionary.Count);

            _dictionary.Add("one", "first value");
            _dictionary.Add("two", "second value");
            _dictionary.Add("three", "third value");
            Assert.AreEqual(3, _dictionary.Count);
        }