[android][espresso] Assert that a View contains a given number of matching views.

EspressoViewCountAssertion.java

/**
 * Sugar for has(int, isAssignableFrom(Class)).
 * 
 *  Example: onView(rootView).check(has(3, EditText.class);
 */
public static ViewAssertion has(final int expectedCount, Class<? extends View> clazz) {
  return has(expectedCount, isAssignableFrom(clazz));
}

/**
 * Returns a generic {@link ViewAssertion} that asserts that there is a
 * given number of descendant views that match the specified matcher.
 * 
 * Example: onView(rootView).check(has(3, isAssignableFrom(EditText.class));
 * 
 * @param expectedCount the number of descendant views that should match the specified matcher
 * @param selector the matcher to select the descendant views
 * @throws AssertionError if the number of views that match the selector is different from expectedCount
 */
public static ViewAssertion has(final int expectedCount, final Matcher<View> selector) {
  return new ViewAssertion() {
    @Override
    public void check(Optional<View> view, Optional<NoMatchingViewException> noViewFoundException) {
      checkArgument(view.isPresent());
      View rootView = view.get();

      Iterable<View> descendantViews = breadthFirstViewTraversal(rootView);
      List<View> selectedViews = new ArrayList<View>();
      for (View descendantView : descendantViews) {
        if (selector.matches(descendantView)) {
          selectedViews.add(descendantView);
        }
      }

      if (selectedViews.size() != expectedCount) {
        String errorMessage = HumanReadables.getViewHierarchyErrorMessage(rootView,
            Optional.of(selectedViews),
            String.format("Found %d views instead of %d matching: %s", selectedViews.size(), expectedCount, selector),
            Optional.of("****MATCHES****"));
        throw new AssertionFailedError(errorMessage);
      }
    }
  };
}