Add test for filters

[Hellowlol]

So we are sure we got them all.

[blacktwin]

I think I found how to get each libraries filters

# ~plexapi.library.LibrarySection
    def _filters(self):
        """ Returns a list of :class:`~plexapi.library.Filter` from this library section. """
        key = '/library/sections/%s/filters' % self.key
        return self.fetchItems(key, cls=Filter)

# ~plexapi.library
class Filter(PlexObject):
    """ Represents a single Filter.

        Attributes:
            TAG (str): 'Directory'
            TYPE (str): 'filter'
    """
    TAG = 'Directory'
    TYPE = 'filter'

    def _loadData(self, data):
        self._data = data
        self.filter = data.attrib.get('filter')
        self.filterType = data.attrib.get('filterType')
        self.key = data.attrib.get('key')
        self.title = data.attrib.get('title')
        self.type = data.attrib.get('type')

I can tack this on to an open PR or wait for some of my PR's to merge before add this.

[blacktwin]

plex.library.section('Music').listChoices('filters') is able to do the same task as the above code...
Also I found that /library/sections/{SECTION_KEY}/filters?includeMeta=1 exposes the library's filters, sorting, fields, and operators. I'm just not sure how to add this.

Here is the janky code I've been playing with.

# ~plexapi.library.LibrarySection
    def _meta(self):
        fields = []
        sorts = []
        filters = []
        fieldTypes = []
        key = '/library/sections/%s/filters?includeMeta=1' % self.key
        data = self._server.query(key)
        for item in data.iter('Type'):
            filters += self.findItems(item, Filter)
            sorts += self.findItems(item, Sort)
            fields += self.findItems(item, Field)
        for item in data.iter('Meta'):
            fieldTypes += self.findItems(item)

        return filters, sorts, fields, fieldTypes

# ~plexapi.library
@utils.registerPlexObject
class Sort(PlexObject):
    """ Represents a

    """
    TAG = 'Sort'

    def _loadData(self, data):
        """ Load attribute values from Plex XML response. """
        self._data = data
        self.defaultDirection = data.attrib.get('defaultDirection')
        self.descKey = data.attrib.get('descKey')
        self.key = data.attrib.get('key')
        self.title = data.attrib.get('title')


@utils.registerPlexObject
class Field(PlexObject):
    """ Represents a

    """
    TAG = 'Field'

    def _loadData(self, data):
        """ Load attribute values from Plex XML response. """
        self._data = data
        self.key = data.attrib.get('key')
        self.title = data.attrib.get('title')
        self.type = data.attrib.get('type')


@utils.registerPlexObject
class Operator(PlexObject):
    """ Represents a

    """
    TAG = 'Operator'

    def _loadData(self, data):
        """ Load attribute values from Plex XML response. """
        self.key = data.attrib.get('key')
        self.title = data.attrib.get('title')


@utils.registerPlexObject
class FieldType(PlexObject):
    """ Represents a

    """
    TAG = 'FieldType'

    def _loadData(self, data):
        """ Load attribute values from Plex XML response. """
        self._data = data
        self.type = data.attrib.get('type')
        self.operators = self.findItems(data, Operator)

I'm hoping that this information can be used to auto populate ALLOWED_FILTERS and ALLOWED_SORT for the different section type classes, along with adding control for operators for searching using Plex.

[blacktwin]

#518 covers this.