public void Fibonacci_ShouldReturn_CorrectIndex_FromSeries()
        {
            var expectedResult = 21;

            _calculations.GetFibonacciNumber(Arg.Any <long>()).Returns(expectedResult);
            var actionResult  = _valuesController.Fibonacci(8);
            var contentResult = actionResult as OkNegotiatedContentResult <string>;

            Assert.IsNotNull(contentResult);
            Assert.AreEqual(Convert.ToInt64(contentResult.Content), expectedResult);
        }