public int GetLetterCountRecursive_ParametersAreValid_ReturnsCharsCount(string str)
 {
     // Act
     return(DoWhileMethods.GetLetterCountRecursive(str));
 }
 public void GetLetterCountRecursive_StrIsNull_ThrowsException()
 {
     // Act
     Assert.Throws <ArgumentNullException>(() => DoWhileMethods.GetLetterCountRecursive(null));
 }