'Test Schema.to_schema_type method for type String.'

def test_to_schema_type_string(self):

    schema = constraints.Schema('String')
    res = schema.to_schema_type('one')
    self.assertIsInstance(res, six.string_types)
    res = schema.to_schema_type('1')
    self.assertIsInstance(res, six.string_types)
    res = schema.to_schema_type(1)
    self.assertIsInstance(res, six.string_types)
    res = schema.to_schema_type(True)
    self.assertIsInstance(res, six.string_types)
    res = schema.to_schema_type(None)
    self.assertIsInstance(res, six.string_types)
