Using MockWebServer with Robolectric - junit

Question

I'm trying to unit test some API calls using MockWebServer and Robolectric.
My test class is annotated with:
#RunWith(RobolectricGradleTestRunner.class)
#Config(constants = BuildConfig.class, sdk = 23)
However when trying to build the Retrofit instance I get the following exception:
java.lang.NullPointerException
at android.os.Handler.__constructor__(Handler.java:229)
at android.os.Handler.<init>(Handler.java)
at retrofit2.Platform$Android$MainThreadExecutor.<init>(Platform.java:105)
at retrofit2.Platform$Android.defaultCallbackExecutor(Platform.java:97)
at retrofit2.Retrofit$Builder.build(Retrofit.java:556)
The code I'm using to build the retrofit instance:
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(mMockServer.url(""))
.addConverterFactory(GsonConverterFactory.create())
.build();
The exception above is returned upon calling .build().
How do I fix this problem?

Answer 1

I had this same problem. There is a bug open about the underlying cause here but while that is ongoing, I settled for using Robolectric 3.0 and the solution outlined by dave-r12 here which is to create the mock I've included below.
#RunWith(RobolectricGradleTestRunner.class)
#Config(shadows = CreateOkHttpClientTest.MyNetworkSecurityPolicy.class)
public class CreateOkHttpClientTest {
#Test
...
#Implements(NetworkSecurityPolicy.class)
public static class MyNetworkSecurityPolicy {
#Implementation
public static NetworkSecurityPolicy getInstance() {
try {
Class<?> shadow = MyNetworkSecurityPolicy.class.forName("android.security.NetworkSecurityPolicy");
return (NetworkSecurityPolicy) shadow.newInstance();
} catch (Exception e) {
throw new AssertionError();
}
}
#Implementation
public boolean isCleartextTrafficPermitted() {
return true;
}
}
}

Answer 2

An alternate solution that seems to work is to just provide a dummy executor when setting up Retrofit
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("http://www.example.com/")
.client(client)
.callbackExecutor(new Executor() {
#Override
public void execute(Runnable command) {
//doesn't matter since tests are synchronous
}
})
.addConverterFactory(ScalarsConverterFactory.create())
.build();
It may be something that in the end needs to be corrected on the Retrofit side, somehow detecting if the current Platform is Robolectric and return a dummy executor or something.

Answer 3

If you are stuck on Robolectric 3 or below and you are targeting the API 25 the proper solution is almost the same like accepted one.
#Implements(NetworkSecurityPolicy.class)
public class NetworkSecurityPolicyShadow {
#Implementation
public static NetworkSecurityPolicy getInstance() {
try {
Class<?> shadow = Class.forName("android.security.NetworkSecurityPolicy");
return (NetworkSecurityPolicy) shadow.newInstance();
} catch (Exception e) {
throw new AssertionError();
}
}
#Implementation
public boolean isCleartextTrafficPermitted(String host) {
return true;
}
}
Only difference is in isCleartextTrafficPermitted(String host) because the OkHttp will try to call this method with host argument.

Answer 4

Could you try with sdk=21. I believe support for sdk=23 was added only from 3.1-SNAPSHOT and not release version.
Edit: I was wrong support was added from version 3.1 because I could successfully run a test
#RunWith(RobolectricGradleTestRunner.class)
#Config(constants = BuildConfig.class, sdk = 23)
public class ExampleUnitTest {
private MockWebServer mMockServer = new MockWebServer();
#Test
public void build_retrofit() throws Exception {
Retrofit retrofit = new Retrofit.Builder()
.baseUrl(mMockServer.url(""))
.addConverterFactory(GsonConverterFactory.create())
.build();
}
}
My gradle.build
testCompile 'junit:junit:4.12'
testCompile "org.robolectric:robolectric:3.1"
testCompile 'com.squareup.okhttp3:mockwebserver:3.3.0'
compile 'com.squareup.retrofit2:retrofit:2.1.0'
compile 'com.squareup.retrofit2:converter-gson:2.1.0'
Which libraries version are you using?