public async Task RetrieveToken_ExpiredAccessToken_ReturnsExpired()
        {
            var accessToken = "token1";

            var cacheMock = new Mock <ITokenCache>();

            var handler = TokenHandler.ExpiredToken();

            Func <HttpClient> clientFactory = () => new HttpClient(handler)
            {
                BaseAddress = new Uri("http://dummy")
            };

            var sut = new RestTokenProvider(clientFactory, cacheMock.Object);

            sut.Initialize(null, null, new Mock <ILogger>().Object);
            var tokenResult = await sut.RetrieveTokenAsync(accessToken);

            Assert.IsFalse(tokenResult.Success);
            Assert.IsTrue(tokenResult.Expired);
        }