8.1.2. Decorator delegate injection points, the following spec paragraph should be tested:

The delegate injection point must be an injected field, initializer method parameter or bean constructor method parameter. If an injection point that is not an injected field, initializer method parameter or bean constructor method parameter is annotated @Delegate, the container automatically detects the problem and treats it as a definition error.

However, TimestampLogger does not declare a valid delegate injection point. As a result, a definition error may be thrown for another reason (see other paragraphs in the same section). Note that decorators cannot declare producers so a definition error may still be thrown for another reason (nothing we can do about).