public async Task FillCacheWithRates_CallExchangeServiceAndCacheService_ExactlyHowManyIsPairsBetweenCurrencies()
{
var allValues = Enum.GetValues(typeof(SupportedCurrencies)).Cast <SupportedCurrencies>()
.Select(x => x.ToString()).ToList();
var numberOfPairs = allValues.SelectMany(x => allValues, (From, To) => new { From, To }).Count();
_exchangeClientMock.Setup(x => x.GetExchangeRate(It.IsAny <string>(), It.IsAny <string>()))
.ReturnsAsync(new CurrencyRateDto());
var sut = new CurrencyService(_distributedCacheServiceMock.Object, _exchangeClientMock.Object);
await sut.FillCacheWithRates();
_exchangeClientMock.Verify(x => x.GetExchangeRate(It.IsAny <string>(), It.IsAny <string>()), Times.Exactly(numberOfPairs));
_distributedCacheServiceMock.Verify(x => x.Set <CurrencyRateDto>(It.IsAny <string>(), It.IsAny <CurrencyRateDto>(), It.IsAny <TimeSpan>()), Times.Exactly(numberOfPairs));
}
