Android: How can i unit test Rxjava Observable?

Question

I'm studying android unit testing and i'm a bit stuck of unit testing for rxjava observable.

This method i'm trying to test:

    @Override
    public Observable<AuthenticationUsingSqlEntity> logInUsingSql(String token, String ssid) {
        SqlRepo sqlRepo = new SqlRepo();
        return sqlRepo.authenticate(token, ssid);
    }

I have created simple ArgumentCaptor to test that input already the same and have been passed on unit testing what i'm trying to do is to test sql retrofit response but i can't.

Answer 1

I wonder why you provide some method call, but not the actual SqlRepo method to test? The result is, that this only permits for a general answer. And it's unclear, which version you're talking about; I'd assume version 2. However, one can simply chain Observable with .test(), in order to test the Observable itself and there's TestObserver, but there's also TestSubscriber, which can be used to test subscribers and TestScheduler, which can be used to schedule mock RX events. It should be obvious, that the method call which've provided will not suffice to write a proper test, as the method to test is entirely unknown (to me).

Answer 2

In your test on that method, you shouldn't use ArgumentCaptor. Normally, it is used when you need to write a test on a method which receives or creates an object and you want to check the validity of that object as a parameter (for example, that an email address is formatted correctly).

// Create a mock of the OtherClass
OtherClass other = mock(OtherClass.class);
    
// Run the foo method with the mock
new A().foo(other);
    
// Capture the argument of the doSomething function
ArgumentCaptor<SomeData> captor = ArgumentCaptor.forClass(SomeData.class);
verify(other, times(1)).doSomething(captor.capture());
    
// Assert the argument
SomeData actual = captor.getValue();
assertEquals("Some inner data", actual.innerData);

The only test on that method that you can use is a test that checks if the method calls sqlRepo.authenticate. If you want to check the response from Retrofit, then you need to write a test specifically on the method 'authenticate' in the class SqlRepo. Also, if you want to write a test specifically on Observable, then you can use TestObserver. You can then use various methods to check the result you'll receive.

Here's an example:

someService.authenticate()
.test()
.assertNoErrors()
.assertValue( someValue -> 
//check if the value is correct
);

Answer 3

Assuming your class is similar to following:

class LoginManager {

 @Override
    public Observable<AuthenticationUsingSqlEntity> logInUsingSql(String token, String ssid) {
        SqlRepo sqlRepo = new SqlRepo();
        return sqlRepo.authenticate(token, ssid);
    }
}

then with unit testing we are aiming to verify the logic of a unit or function.

in that perspective the logic of your method is that you we offload the login operation to SqlRepo class. And we have to verify this logic. So as to do that we check whether authenticate function of Sqlrepo is being invoked in response to the invokation of logInUsingSql() method. we do that by :

 loginManagerClassUnderTest = Mockito.spy(loginManagerClassUnderTest);
 mockSqlRepo mockSqlRepo = Mockito.mock(mockSqlRepo.class);
 doReturn(mockSqlRepo).when(loginManagerClassUnderTest).getSqlRepo();
 loginManagerClassUnderTest.logInUsingsql("mockToken", "mockSsid");
 ArgumentCaptor<String> tokenCaptor = ArgumentCaptor.forClass(String.class);
 ArgumentCaptor<String> ssidCaptor = ArgumentCaptor.forClass(String.class);
 verify(mockSqlRepo).authenticate(tokenCaptor.capture(), ssidCaptor.capture());
 assertEquals("mockToken", tokenCaptor.getValue());
 assertEquals("mockSsid", ssidCaptor.getValue());

As you can see that LoginManager is dependent on SqlRepo class and we have to provide a mock for this dependency so that we ensure that test is carried out in isolation. so change Loginmanager Function to :

 class LoginManager {
    
     @Override
        public Observable<AuthenticationUsingSqlEntity> logInUsingSql(String token, String ssid) {
            SqlRepo sqlRepo = getSqlRepo();
            return sqlRepo.authenticate(token, ssid);
        }

     public SqlRepo getSqlRepo() {
        return new SqlRepo();
     }
  }