Android, Room fail on unit testing with Robolectric

Question

I am trying to create some tests for a view model.

The view model includes a Database instantiation which calls a Database

CallRoomDatabase db = CallRoomDatabase.getDatabase(application);

where getDatabase takes an instance of the Dao()

  @Database(entities = {CallEntity.class}, version = 1)
 public abstract class CallRoomDatabase extends RoomDatabase {

public abstract CDao cDao();

// marking the instance as volatile to ensure atomic access to the variable
private static volatile CRoomDatabase INSTANCE;

public static CRoomDatabase getDatabase(final Context context) {
    if (INSTANCE == null) {
        synchronized (CallRoomDatabase.class) {
            if (INSTANCE == null) {
                INSTANCE = Room.databaseBuilder(context.getApplicationContext(),
                        CRoomDatabase.class, "database")
                        // Wipes and rebuilds instead of migrating if no Migration object.
                        // Migration is not part of this codelab.
                        .fallbackToDestructiveMigration()
                        .addCallback(sRoomDatabaseCallback)
                        .build();
            }
        }
    }
    return INSTANCE;
}

However, when trying to instantiate the model within a test, I get an error on .build() above

  java.lang.NullPointerException
at androidx.room.Room.getGeneratedImplementation(Room.java:79)
at androidx.room.RoomDatabase$Builder.build(RoomDatabase.java:952)
at com.s.o.dbutils.CRoomDatabase.getDatabase(CRoomDatabase.java:32)
at com.s.o.viewmodels.CViewModelTest.checkForNuTest(CViewModelTest.kt:66)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
at org.powermock.modules.junit4.rule.PowerMockStatement$1.run(PowerMockRule.java:83)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)

At RoomDatabase.java

            T db = Room.getGeneratedImplementation(mDatabaseClass, DB_IMPL_SUFFIX);

At Room.java klass is null

        static  T getGeneratedImplementation(Class klass, String suffix) {

I have tried not using the model at all at the test, just instantiate the db with

          val db = CRoomDatabase.getDatabase(ApplicationProvider.getApplicationContext())

Still breaks at the same .build()

Any ideas how to get past that exception ?

We dont actually need to test the db someway, just some functions included in that model, so some way to just avoid the error would suffice.

user_5644761 · Answer

Room should be tested as an Android Instrumentation Test, not a JUnit test.

Update:

Use mockito to mock the database and any repositories.

Utilise mockito methods like:

@Mock - Mocking annotation to mock global and local variables.
mock - Initiate a mock of a class in-line.
when - configure return behavior for mock.
verify - Assert interactions on mocks and their methods.
times - Used with verify to assert number of calls to a mock and it's method.
any - An argument matcher for asserting provided values to mocks.

Using Mockito, example. I don't know how your code works, i made some assumptions like the existence of a Call.class and what mocks you would require:

@Mock private CallRoomDatabase database;
@Mock private CRoomDatabase cRoomDatabase;
@Mock private CDao cDao;

private MyClass myClass;

@Before 
public void setUp() {
    // initiate all globally defined mocks annotated with @Mock
    initMocks(this);

    // Setup our expected behaviour from the mock
    when(database.getDatabase()).thenReturn(cRoomDatabase);
    myClass = new myClass(database, cDao);
}

@Test 
public void givenSomeTest_whenCallingGetCall_thenInsertNewCall() {
    // Setup our expected behaviour from the mock
    when(cDao.getCall()).thenReturn(mock(Call.class));

    // do test

    // assert mock interaction with arguments and number of expected calls
    verify(cDao, times(1)).insertCall(any(mock(Call.class)))
}

user_13012929 · Answer

To test the program in isolation from the database, I recommend implementing 2 repositories: 1 repository for the project, 1 for testing and a common interface for them. You can implement this using Dagger 2.

Android, Room fail on unit testing with Robolectric

2 Answers