def METHOD_NAME(empty_data_folder, a_key, a_tpub_only_key):
    # A DeviceManager manages devices, specifically the persistence
    # of them via json-files in an empty data folder
    dm = DeviceManager(data_folder=empty_data_folder)
    # initialization will load from the folder but it's empty at first
    assert len(dm.devices) == 0
    # a device has a name, a type and a list of keys
    a_key = Key(
        "Vpub5n9kKePTPPGtw3RddeJWJe29epEyBBcoHbbPi5HhpoG2kTVsSCUzsad33RJUt3LktEUUPPofcZczuudnwR7ZgkAkT6N2K2Z7wdyjYrVAkXM",
        "08686ac6",
        "m/48h/1h/0h/2h",
        "wsh",
        "",
        "tpubDFHpKypXq4kwUrqLotPs6fCic5bFqTRGMBaTi9s5YwwGymE8FLGwB2kDXALxqvNwFxB1dLWYBmmeFVjmUSdt2AsaQuPmkyPLBKRZW8BGCiL",
    )
    # the DeviceManager doesn't care so much about the content of a key
    # so let's add two keys:
    dm.add_device("some_name", "the_type", [a_key, a_tpub_only_key])
    # A json file was generated for the new device:
    assert os.path.isfile(dm.devices["some_name"].fullpath)
    # You can access the new device either by its name of with `get_by_alias` by its alias
    assert dm.get_by_alias("some_name").name == "some_name"
    # unknown device is replaced by 'other'
    assert dm.get_by_alias("some_name").device_type == "other"
    assert dm.get_by_alias("some_name").keys[0].fingerprint == "08686ac6"
    # Now it has a length of 1
    assert len(dm.devices) == 1
    # and is iterable
    assert [the_type.device_type for the_type in dm.devices.values()] == ["other"]
    # The DeviceManager will return Device-Types (subclass of dict)
    # any unknown type is replaced by GenericDevice
    assert type(dm.devices["some_name"]) == GenericDevice
    # The DeviceManager also has a `devices_names` property, returning a sorted list of the names of all devices
    assert dm.devices_names == ["some_name"]
    dm.add_device("another_name", "the_type", [a_key, a_tpub_only_key])
    assert dm.devices_names == ["another_name", "some_name"]
    # You can also remove a device - which will delete its json and remove it from the manager
    another_device_fullpath = dm.devices["another_name"].fullpath
    assert os.path.isfile(another_device_fullpath)
    dm.remove_device(dm.devices["another_name"])
    assert not os.path.isfile(another_device_fullpath)
    assert len(dm.devices) == 1
    assert dm.devices_names == ["some_name"]
    # A device is mainly a Domain-Object which assumes an underlying
    # json-file which can be found in the "fullpath"-key
    # It derives from a dict
    # It needs a DeviceManager to be injected and can't reasonable
    # be created on your own.
    # It has 5 dict keys: `fullpath`, `alias`, `name`, `type`, `keys`
    some_device = dm.devices["some_name"]
    assert some_device.fullpath == empty_data_folder + "/some_name.json"
    assert some_device.alias == "some_name"
    assert some_device.name == "some_name"
    assert some_device.device_type == "other"
    assert len(some_device.keys) == 2
    assert some_device.keys[0] == a_key
    assert some_device.keys[1] == a_tpub_only_key
    # Keys can be added and removed. It will instantly update the underlying json
    # Adding keys can be done by passing an array of keys object to the `add_keys` method of a device
    # A key dict must contain an `original` property
    third_key = Key.from_json(
        {
            "original": "tpubDEmTg3b5aPNFnkHXx481F3h9dPSVJiyvqV24dBMXWncoRRu6VJzPDeEtQ4H7EnRtLbn2aPkxhTn8odWXsXkSRDdmAvCCrPmfjfPSVswfDhg"
        }
    )
    some_device.add_keys([third_key])
    assert len(some_device.keys) == 3
    assert some_device.keys[0] == a_key
    assert some_device.keys[1] == a_tpub_only_key
    assert some_device.keys[2] == third_key
    # adding an existing key will do nothing
    some_device.add_keys([third_key])
    assert len(some_device.keys) == 3
    assert some_device.keys[0] == a_key
    assert some_device.keys[1] == a_tpub_only_key
    assert some_device.keys[2] == third_key
    # Removing a key can be done by passing the `original` property of the key to remove to the `remove_key` method of a device
    some_device.remove_key(third_key)
    assert len(some_device.keys) == 2
    assert some_device.keys[0] == a_key
    assert some_device.keys[1] == a_tpub_only_key
    # removing a none existing key will do nothing
    some_device.remove_key(third_key)
    assert len(some_device.keys) == 2
    assert some_device.keys[0] == a_key
    assert some_device.keys[1] == a_tpub_only_key