public void CanFakeMyHttpClient() { // Arrange var fakeHttpClientWrapper = A.Fake <IHttpClientWrapper>(); var TestResults = "Fake Response Data for Test"; A.CallTo(() => fakeHttpClientWrapper.Get(A <string> .That.Matches(s => s == Config.ApiEndpoint))) .Returns(Task.FromResult(new HttpResponseMessage { StatusCode = HttpStatusCode.OK, Content = new StringContent(TestResults) })); var client = new ClientClass(new ServiceClass(fakeHttpClientWrapper)); // Act var result = client.GetStringFromApi(); // Assert Assert.AreEqual(TestResults, result); }