public function test_validate_date_values_second() {
    // Valid values.
    $seconds = range( 0, 59 );
    foreach ( $seconds as $second ) {
      $this->assertTrue( $this->q->validate_date_values( array( 'second' => $second ) ) );
    }

    // Invalid values.
    $seconds = array( -1, 60 );
    foreach ( $seconds as $second ) {
      $this->assertFalse( $this->q->validate_date_values( array( 'second' => $second ) ) );
    }

  }