public void FrequencySortTest() { var s = new Solution(); string input, expected; input = "tree"; expected = "eetr"; Assert.Equal(expected, s.FrequencySort(input)); input = "cccaaa"; expected = "cccaaa"; Assert.Equal(expected, s.FrequencySort(input)); input = "Aabb"; expected = "bbAa"; Assert.Equal(expected, s.FrequencySort(input)); }