unit test for a class with required user arguments in python

I defined a class that as following:

class Parameter(object):
    def  __init__(self ):
            self.parser = ArgumentParser()
            self.parser.add_argument("-db", type = str , action= "store", dest = "database", required=True)   
            self.parser.add_argument("-coll",  type=str,  action="store",  dest="collection",  required=True)
            self.parser.add_argument("-sys",  type=bool,  action="store",  dest="system",  default="TRUE")
            self.args = self.parser.parse_args()


    def checkArgs(self, connect):
            right = True
            with MongoConnection(connect) as conMongo:
                    all_dbs = conMongo.conMongo.database_names()

                    if self.args.database not in all_dbs:
                            right = False
                            raise ValueError("\nThe given database name does not exists.\n" % (self.args.database))
            return right



if __name__ == '__main__':
    connection = 'server connection information'
    params = Parameter()
    try:
            params.checkArgs(connection)
    except ValueError as e:
            print(e)

How can I write a unit test for this Class that checks if the given db name by the user actually exists in the database server?