Multiclass classification task where each class is present only once in the test set
When talking about the test data, we can have any number of examples of each class for inference. It doesn't matter if it has 20 classes with one example each. 

You can use a CNN classifier for this type of a problem but if one book can be written by more than one author you should use sigmoid activation in the last layer rather than using softmax. 

You can see this article which address an usecase similar to yours - Link