DefaultFailureHandler.java

package com.google.android.apps.common.testing.ui.espresso.base;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Throwables.propagate;

import com.google.android.apps.common.testing.testrunner.inject.TargetContext;
import com.google.android.apps.common.testing.ui.espresso.EspressoException;
import com.google.android.apps.common.testing.ui.espresso.FailureHandler;
import com.google.android.apps.common.testing.ui.espresso.PerformException;

import android.content.Context;
import android.view.View;

import junit.framework.AssertionFailedError;

import org.hamcrest.Matcher;

import java.util.concurrent.atomic.AtomicInteger;

import javax.inject.Inject;

/**
 * Espresso's default {@link FailureHandler}. If this does not fit your needs, feel free to provide
 * your own implementation via Espresso.setFailureHandler(FailureHandler).
 */
public final class DefaultFailureHandler implements FailureHandler {

  private static final AtomicInteger failureCount = new AtomicInteger(0);
  private final Context appContext;

  @Inject
  public DefaultFailureHandler(@TargetContext Context appContext) {
    this.appContext = checkNotNull(appContext);
  }

  @Override
  public void handle(Throwable error, Matcher<View> viewMatcher) {
    if (error instanceof EspressoException || error instanceof AssertionFailedError
        || error instanceof AssertionError) {
      throw propagate(getUserFriendlyError(error, viewMatcher));
    } else {
      throw propagate(error);
    }
  }

  /**
   * When the error is coming from espresso, it is more user friendly to:
   * 1. propagate assertions as assertions
   * 2. swap the stack trace of the error to that of current thread (which will show
   * directly where the actual problem is)
   */
  private Throwable getUserFriendlyError(Throwable error, Matcher<View> viewMatcher) {
    if (error instanceof PerformException) {
      // Re-throw the exception with the viewMatcher (used to locate the view) as the view
      // description (makes the error more readable). The reason we do this here: not all creators
      // of PerformException have access to the viewMatcher.
      throw new PerformException.Builder()
        .from((PerformException) error)
        .withViewDescription(viewMatcher.toString())
        .build();
    }

    if (error instanceof AssertionError) {
      // reports Failure instead of Error.
      // assertThat(...) throws an AssertionFailedError.
      error = new AssertionFailedWithCauseError(error.getMessage(), error);
    }

    error.setStackTrace(Thread.currentThread().getStackTrace());
    return error;
  }

  private static final class AssertionFailedWithCauseError extends AssertionFailedError {
    /* junit hides the cause constructor. */
    public AssertionFailedWithCauseError(String message, Throwable cause) {
      super(message);
      initCause(cause);
    }
  }
}