Simulate no network using Retrofit and MockWebServer

Question

I want to simulate the no network case when using RetroFit and MockWebServer.

Im currently testing using Espresso and supplying the MockWebServers url to the RestAdapter before I start my tests. This works great for mocking server responses and so on but I cant see a simple way to script the java.net.ConnectException exception thrown when a device has no network. I can see the MockResponse allows throttling simulation and so on but not a custom exception.

I know I could go the root of mocking the actual web api interface used by retrofit but I would like to use the same approach as my other tests if possible by using MockWebServer.

I imagine I've just missed something simple :)

Thanks

score 30 · Accepted Answer · edited May 16 '16 at 16:44

30

Retrofit has a retrofit-mock module which offers a MockRestAdapter class whose purpose is to simulate network delay and errors.

This is a used in conjunction with the normal RestAdapter to create an instance of your service. You can see a full example in the samples/mock-github-client/ folder of the repo: https://github.com/square/retrofit/tree/parent-1.9.0/retrofit-samples/mock-github-client

MockRestAdapter offers these APIs:

setDelay - Set the network round trip delay, in milliseconds.
setVariancePercentage - Set the plus-or-minus variance percentage of the network round trip delay.
setErrorPercentage - Set the percentage of calls to calculateIsFailure() that return true.

In your test, you can call setErrorPercentage(100) to guarantee that a network error will occur. By default the amount of time for the error to be thrown is anywhere from 0 to 3x the delay. Set the delay to 0 for instant results.

edited May 16 '16 at 16:44

Diego Palomar

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answered Jul 25 '14 at 16:23

Jake Wharton

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The link is broken :( – Alireza Farahani Nov 11 '15 at 13:05
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Updated link: https://github.com/square/retrofit/blob/master/retrofit-mock/src/test/java/retrofit2/mock/MockRetrofitTest.java – Jan 08 '16 at 21:37
Sir,i try to override the baseurl of retrofit to the one from mockwebserver, but then i still end up making a webservice call when performing the test, is there a way to stop that? Please assist. @tony19, Jake Wharton – Rat-a-tat-a-tat Ratatouille Mar 25 '16 at 21:17

score 15 · Answer 2 · answered Apr 02 '20 at 08:55

The easiest way to simulate network issues with MockWebServer is by setting the SocketPolicy to SocketPolicy.DISCONNECT_AT_START, SocketPolicy.NO_RESPONSE or etc:

MockWebServer server = new MockWebServer();

MockResponse response = new MockResponse()
  .setSocketPolicy(SocketPolicy.DISCONNECT_AT_START);

server.enqueue(response);

This way you can simulate network errors like connection prematurely closed before response or Timeout exceptions

score 7 · Answer 3 · edited May 23 '17 at 12:17

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to be clear with whe types of exceptions here you can see the differences:

Internet Connection Error

So you can get two types:

UnknownHostException - When you don't have internet or unknown host... to simulate this, set to the adapter an incorrect end point.

ConnectException - mockwebserver can throw a timeout exception. You can see how to do it here:

https://github.com/square/okhttp/tree/master/mockwebserver

Really I don't know how your code is, but I hope this is useful

edited May 23 '17 at 12:17

Community

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answered Jul 25 '14 at 12:18

mromer

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+1 thanks for answering but it does not really answer the question as I want to simulate no network as opposed to a timeout. Dispatchers interesting though. I wonder if i can throw the above exceptions though that... – Dori Jul 25 '14 at 12:33
seems I cant as the network exceptions are checked and the dispatcher only throws Inturrupted as per its interface – Dori Jul 25 '14 at 13:24

Jesús Castro · Answer 4 · 2015-02-19T14:52:28.153

I don't know if it's useful, but you can simulate a timeout with MockWebServer:

String contentType = "Content-type: application/json";
MockResponse response = MockResponse().setResponseCode(statusCode).setBody(responseBody).addHeader(contentType);
MockWebServer proxy = new MockWebServer();
proxy.enqueue(response);
proxy.setBodyDelayTimeMs(timeoutDelay));
proxy.play(10000); //Number port - Important!!!

Note: Please, set HttpClient of your code (e.g. AsyncHttpClient) with that number port for testing purpose.

score 3 · Answer 5 · answered May 30 '19 at 08:19

What worked for me is pointing the Retrofit URL (end-point) to a random non-existent host . I used "thisIsARandomHost.com" and bingo i was able to mock the unknown host exception.

For example : setAPP_URL = "http://thisIsARandomHost.com/";

Here , setAPP_URL is the string variable that contains my url which I pass on to retrofit , when I want to mock unknown host exception in my tests I set the url as above .For all other purposes it is set to the valid URL required by my app.

As stated in above answers , MockWebServer is a great library for mocking retrofit responses , but you don't need that library for mocking this exception . For mocking all other exceptions I would recommend MockWebServer , I use it a lot in my project for testing responses.

Note : You can set the app url to anything as long as that url doesn't exist on the web.

score 1 · Answer 6 · answered Sep 21 '21 at 16:43

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mockWebServer.shutdown() before executing your unit test is fine.

Internally it closes the socket connection:

serverSocket!!.close()

answered Sep 21 '21 at 16:43

Michał Dobi Dobrzański

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Simulate no network using Retrofit and MockWebServer

6 Answers6