public void AddRefreshTokenCheckWhenRefreshTokenNotExist_Test()
        {
            _refreshTokenRepositoryMock.Setup(repo => repo.GetAsync(It.IsAny <System.Linq.Expressions.Expression <Func <RefreshTokens, bool> > >())).Returns(async() => { return(null); });

            _refreshTokenRepositoryMock.Setup(repo => repo.InsertAsync(refreshTokenInitialize)).Returns(async() => { return(refreshTokenInitialize); });

            var result = _refreshTokenService.AddRefreshTokenAsync(RefreshToken, UserId, DaysToExpire);

            Assert.IsTrue(result.IsCompleted);
        }