Class C

Lib/test/test_zstd.py:1779–1781

        # 3, no .fileno() method
        class C:
            def read(self, size=-1):
                return b'123'
        with ZstdFile(C(), 'rb') as f:
            with self.assertRaisesRegex(AttributeError, r'fileno'):
                f.fileno()