@Override
    protected MockServer buildMockServer() {
        return new MockServer(MockServer.DummyResponseServerBehavior.build(200, "OK", "Hi"));
    }
This class starts a mock proxy server, and once a request is sent to this mock proxy server,
a 200 OK will be returned. We'll take advantage of this returned status code to test whether
a request to the given fake service host is passed through the proxy or not.
aws-java-sdk-core/src/test/java/com/amazonaws/internal/SdkProxyRoutePlannerIntegrationTest.java