def METHOD_NAME(self):
    mod = self.make_module("""
        HPyDef_METH(f, "f", HPyFunc_O)
        static HPy f_impl(HPyContext *ctx, HPy self, HPy arg)
        {
            const char *buf;
            buf = HPyBytes_AsString(ctx, arg);
            return HPyBytes_FromString(ctx, buf);
        }
        @EXPORT(f)
        @INIT
    """)
    assert mod.f(b"aaa") == b"aaa"
    assert mod.f(b"") == b""