public async Task TestRestGreetingProvider(string expectedGreeting)
{
var httpClientFactoryMock = Substitute.For <IHttpClientFactory>();
var fakeHttpMessageHandler = FakeHttpMessageHandler.FactoryWithJsonBody(expectedGreeting);
var fakeHttpClient = new HttpClient(fakeHttpMessageHandler);
httpClientFactoryMock.CreateClient().Returns(fakeHttpClient);
var greetingProvider = new RestGreetingProvider(Substitute.For <ILogger <RestGreetingProvider> >(), httpClientFactoryMock, FactoryServicesConfig());
(await greetingProvider.GetGreeting())
.Should().Be(expectedGreeting);
}