public function test_validate_date_values_hour() {
    // Valid values.
    $hours = range( 0, 23 );
    foreach ( $hours as $hour ) {
      $this->assertTrue( $this->q->validate_date_values( array( 'hour' => $hour ) ) );
    }

    // Invalid values.
    $hours = array( -1, 24, 25, 'string' );
    foreach ( $hours as $hour ) {
      $this->assertFalse( $this->q->validate_date_values( array( 'hour' => $hour ) ) );
    }
  }