I did read the article.

so for less than a year the formula is just the rate of return absolute itself right?

now there is a test case called testCalculateAnnualizedReturnGoogl which gives values 1054.00, 1348.00 as buy and sell respectively . if we apply the formula (sell_value - buy_value) / buy_value we get 0.2789373814 manually . Why is it expecting 0.298?