Test that the widget definition functions work.
function testWidgetDefinition() {
$widget_definition = field_info_widget_types('test_field_widget_multiple');
// Test if hook_field_widget_info_alter is beïng called.
$this
->assertTrue(in_array('test_field', $widget_definition['field_types']), "The 'test_field_widget_multiple' widget is enabled for the 'test_field' field type in field_test_field_widget_info_alter().");
}