public function test_validate_date_values_day_of_week_iso() {
    // Valid values.
    $days_of_week = range( 1, 7 );
    foreach ( $days_of_week as $day_of_week ) {
      $this->assertTrue( $this->q->validate_date_values( array( 'dayofweek_iso' => $day_of_week ) ) );
    }

    // Invalid values.
    $days_of_week = array( -1, 0, 8 );
    foreach ( $days_of_week as $day_of_week ) {
      $this->assertFalse( $this->q->validate_date_values( array( 'dayofweek_iso' => $day_of_week ) ) );
    }
  }