public async Task GetExchangeRatesTest()
        {
            //Arrange
            var repository = new CurrenciesRepository();

            //Act
            var exchangeRates = await repository.GetExchangeRates(DateTime.Now);

            //Assert
            Assert.IsNotNull(exchangeRates);
        }
        public async Task GetCurrencyRateInEuroReturnsNull_IfCacheIsNotEmptyTest()
        {
            //Arrange
            var repository = new CurrenciesRepository();

            //Act
            var exchangeRates = await repository.GetExchangeRates(DateTime.Now);

            var exchangeRate = repository.GetCurrencyRateInEuro("USD", DateTime.Now);

            //Assert
            Assert.IsNotNull(exchangeRate);
        }