Implementation and usage of an IdlingResource that waits for Picasso actions to finish.

Picasso idlingresource.md

Note that the file lives in the package as Picasso. Otherwise we don't have access to targetToAction

package com.squareup.picasso;

public class PicassoIdlingResource implements IdlingResource, ActivityLifecycleCallback {
  protected ResourceCallback callback;

  WeakReference<Picasso> picassoWeakReference;

  @Override
  public String getName() {
    return "PicassoIdlingResource";
  }

  @Override
  public boolean isIdleNow() {
    if (isIdle()) {
      notifyDone();
      return true;
    } else {
      return false;
    }
  }

  public boolean isIdle() {
    return picassoWeakReference == null
            || picassoWeakReference.get() == null
            || picassoWeakReference.get().targetToAction.isEmpty();
  }

  @Override
  public void registerIdleTransitionCallback(ResourceCallback resourceCallback) {
    this.callback = resourceCallback;
  }

  void notifyDone() {
    if (callback != null) {
      callback.onTransitionToIdle();
    }
  }

  @Override
  public void onActivityLifecycleChanged(Activity activity, Stage stage) {
    switch (stage) {
      case CREATED:
        picassoWeakReference = new WeakReference<>(Picasso.with(activity));
        break;
      case STOPPED:
        // Clean up reference
        picassoWeakReference = null;
        break;
      default: // NOP
    }
  }
}

USAGE

  @Before
  protected void setUp() throws Exception {
    super.setUp();
    
    Espresso.registerIdlingResources(mPicassoIdlingResource);

    ActivityLifecycleMonitorRegistry
            .getInstance()
            .addLifecycleCallback(mPicassoIdlingResource);
  }
  
  @After
  protected void tearDown() throws Exception {
    super.tearDown();
    
    Espresso.unregisterIdlingResources(mPicassoIdlingResource);
  }

There's at least one flaw that I know of. If your code passes null as the path to load, this idlingresource does not wait for the placeholder drawable to be used in the ImageView.

I'm sure there are more errors and better ways to implement this, but it's working for my tests.

Hi, I forked this gist and updated it with a couple of improvements to handle multiple Activities and execute tests faster:
https://gist.github.com/sebaslogen/0b2fdea3f322c730e04b0af7285fcd28