How to use the jsonpatch.JsonPatchTestFailed function in jsonpatch

def test_test_error(self):
        obj =  {'bar': 'qux'}
        self.assertRaises(jsonpatch.JsonPatchTestFailed,
                          jsonpatch.apply_patch,
                          obj, [{'op': 'test', 'path': '/bar', 'value': 'bar'}])

if part is None:
                val = subobj
            else:
                val = self.pointer.walk(subobj, part)
        except JsonPointerException as ex:
            raise JsonPatchTestFailed(str(ex))

        try:
            value = self.operation['value']
        except KeyError as ex:
            raise InvalidJsonPatch(
                "The operation does not contain a 'value' member")

        if val != value:
            msg = '{0} ({1}) is not equal to tested value {2} ({3})'
            raise JsonPatchTestFailed(msg.format(val, type(val),
                                                 value, type(value)))

        return obj

def apply(self, obj):
        try:
            subobj, part = self.pointer.to_last(obj)
            if part is None:
                val = subobj
            else:
                val = self.pointer.walk(subobj, part)
        except JsonPointerException as ex:
            raise JsonPatchTestFailed(str(ex))

        try:
            value = self.operation['value']
        except KeyError as ex:
            raise InvalidJsonPatch(
                "The operation does not contain a 'value' member")

        if val != value:
            msg = '{0} ({1}) is not equal to tested value {2} ({3})'
            raise JsonPatchTestFailed(msg.format(val, type(val),
                                                 value, type(value)))

        return obj