public async Task StubIntegration_RegularGet_Dynamic_UtcNow() { // arrange var url = $"{TestServer.BaseAddress}dynamic-utc-now.txt"; const string expectedDateTime = "2019-08-21 20:41:51"; var expectedResult = $"UTC now: {expectedDateTime}"; var now = new DateTime(2019, 8, 21, 20, 41, 51, DateTimeKind.Utc); DateTimeMock .Setup(m => m.UtcNow) .Returns(now); var request = new HttpRequestMessage(HttpMethod.Get, url); // act / assert using var response = await Client.SendAsync(request); var content = await response.Content.ReadAsStringAsync(); Assert.AreEqual(expectedResult, content); Assert.AreEqual(HttpStatusCode.OK, response.StatusCode); Assert.AreEqual("text/plain", response.Content.Headers.ContentType.ToString()); Assert.AreEqual(expectedDateTime, response.Headers.Single(h => h.Key == "X-Header").Value.Single()); }