protected DataSubscriber<Object> verifyGetAndSubscribe(
        Supplier<DataSource<Object>> dataSourceSupplier,
        DataSource<Object> underlyingDataSource,
        boolean expectMoreInteractions) {
      mInOrder.verify(dataSourceSupplier).get();
      ArgumentCaptor<DataSubscriber> captor = ArgumentCaptor.forClass(DataSubscriber.class);
      mInOrder.verify(underlyingDataSource).subscribe(captor.capture(), any(Executor.class));
      if (!expectMoreInteractions) {
        verifyNoMoreInteractionsAll();
      }
      return captor.getValue();
    }
Verifies that our mDataSourceSupplier got underlying data source and subscribed to it.
Subscriber is returned.
fbcore/src/test/java/com/facebook/datasource/DataSourceTestUtils.java