Unit Testable RecyclerViews

When building our Android apps, we can often wind up with a decent amount of code in our RecyclerView.Adapters that we want to test. In this article, I briefly suggest two ways of structuring our RecyclerView-related classes so that we can accomplish this.

First, let’s look at a simple list that’ll serve as a working example:

Simple RecyclerView

Here’s the code that creates this list:

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        final RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(new RecyclerView.Adapter() {
            @Override
            public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
                return new RecyclerView.ViewHolder(new TextView(parent.getContext())) {};
            }

            @Override
            public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
                ((TextView) holder.itemView).setText(String.valueOf(position));
            }

            @Override
            public int getItemCount() {
                return 100;
            }
        });
    }
}

Now that we’ve introduced a working example, let’s look at two ways of making RecyclerView-related code unit testable.

An Obvious Way: MVP

One of the oft-cited benefits of using MVP in Android apps is that it enhances testability. So, a natural way of structuring our RecyclerView related classes so that we can enhance testability is to apply MVP to those classes. To do this, we make the ViewHolder sublcass implement an MVP View.

private static class SimpleListItemViewHolder extends RecyclerView.ViewHolder implements SimpleListItemView {

    SimpleListItemViewHolder(View itemView) {
        super(itemView);
    }

    @Override // From SimpleListItemView interface
    public void setText(String text) {
        ((TextView) itemView).setText(text);
    }
}

Next, we setup our RecyclerView.Adapter to create Presenters for each ViewHolder and we delegate the presentation logic to those presenters in onBindViewHolder:

private static class MyAdapter extends RecyclerView.Adapter<SimpleListItemViewHolder> {

    @Override
    public SimpleListItemViewHolder onCreateViewHolder(ViewGroup parent,
                                                        int viewType) {
        final TextView itemView = new TextView(parent.getContext());
        itemView.setTag(new Presenter());
        return new SimpleListItemViewHolder(itemView);
    }

    @Override
    public void onBindViewHolder(SimpleListItemViewHolder holder, int position) {
        ((Presenter) holder.itemView.getTag()).presentListItem(holder, position);
    }

    //...
}

Notice here that we set the Presenter as a tag on the ViewHolder’s itemView. When it’s time to bind the ViewHolder, we can grab the Presenter from the tag delegate the presentation logic to it. Here’s what the Presenter looks like:

private static class Presenter {
    void presentListItem(SimpleListItemView view, int position) {
        view.setText(String.valueOf(position));
    }
}

Because the logic we want to test now lives inside of the Presenter, a simple POJO, unit testing the presentation logic for our RecyclerViews becomes much easier. We simply instantiate a Presenter, call its main presentation method, and verify that it interacts properly with its MVP View.

public class PresenterTest {
    //...
    @Test
    public void presentListItemShouldSetViewTextToPosition() throws Exception {
        MainActivity.Presenter presenter = new MainActivity.Presenter();

        presenter.presentListItem(mSimpleListItemView, 0);

        verify(mSimpleListItemView).setText("0");
    }
}

A Lighter Way: Reusing a Presenter

Let’s look at another way of making our RecyclerView related classes unit testable. While the above approach works fine, I sometimes find that having to create an extra presenter class that is stored and retrieved as a tag on a ViewHolder’s item view a bit much, especially if I already have a Presenter that is simply responsible for fetching items to display in the list.

Let’s alter our working example a bit to suppose we had such a presenter. Instead of simply displaying the position of a ViewHolder in our RecyclerView, let’s display numbers we have to fetch from somewhere else. In this case, we’ll probably want a (unit-testable)Presenter that looks like this:

static class Presenter {
    private final NumberFetcher mNumberFetcher;
    private final NumberListView mNumberListView;

    Presenter(NumberFetcher numberFetcher, NumberListView numberListView) {
        mNumberFetcher = numberFetcher;
        mNumberListView = numberListView;
    }

    public void onViewReady() {
        mNumberFetcher.getNumbers(new Callback() {

            @Override
            public void onSuccess(List<Integer> numbers) {
                mNumberListView.displayNumbers(numbers);
            }

            @Override
            public void onFailure(Throwable err) {
                mNumberListView.displayErrorMessage();
            }
        });
    }
}

Now, if we were simply using MVP for a RecyclerView-related classes, the highlighted displayNumbers method is where we’d have to create our Adapter that would creat and use a separate Presenter class that would hold our presentation logic. Since we already have a Presenter, however, we can simply reuse it by passing it to the RecyclerView.Adapter via our MVP View method:

static class Presenter {
    //...
    public void onViewReady() {
        mNumberFetcher.getNumbers(new Callback() {
            @Override
            public void onSuccess(List<Integer> numbers) {
                mNumberListView.displayNumbers(numbers, this);
            }
            //...
        });
    }
}

Here’s the implementation of the displayNumbers view:

public class MainActivity extends AppCompatActivity implements NumberListView {
    //...
    @Override
    public void displayNumbers(List<Integer> numbers, Presenter presenter) {
        final RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setAdapter(new MyAdapter(numbers, presenter));
    }
}

And here’s the adapter delegating to the same Presenter that’s responsible for loading the items in the list:

private static class MyAdapter extends RecyclerView.Adapter<SimpleListItemViewHolder> {

        private final List<Integer> mNumbers;
        private final Presenter mPresenter;

        MyAdapter(List<Integer> numbers, Presenter presenter) {
            mNumbers = numbers;
            mPresenter = presenter;
        }

        @Override
        public SimpleListItemViewHolder onCreateViewHolder(ViewGroup parent,
                                                           int viewType) {
            final TextView itemView = new TextView(parent.getContext());
            return new SimpleListItemViewHolder(itemView);
        }

        @Override
        public void onBindViewHolder(SimpleListItemViewHolder holder, int position) {
            mPresenter.presentListItem(holder, position);
        }

        @Override
        public int getItemCount() {
            return mNumbers.size();
        }
    }