public function test_filter_priority() {
    $a   = new MockAction();
    $tag = __FUNCTION__;
    $val = __FUNCTION__ . '_val';

    // Make two filters with different priorities.
    add_filter( $tag, array( $a, 'filter' ), 10 );
    add_filter( $tag, array( $a, 'filter2' ), 9 );
    $this->assertSame( $val, apply_filters( $tag, $val ) );

    // There should be two events, one per filter.
    $this->assertSame( 2, $a->get_call_count() );

    $expected = array(
      // 'filter2' is called first because it has priority 9.
      array(
        'filter' => 'filter2',
        'tag'    => $tag,
        'args'   => array( $val ),
      ),
      // 'filter' is called second.
      array(
        'filter' => 'filter',
        'tag'    => $tag,
        'args'   => array( $val ),
      ),
    );

    $this->assertSame( $expected, $a->get_events() );
  }