Add the action to get author's books.

test/decentralised_book_index/metadata/book_test.exs

@@ -59,4 +59,18 @@ defmodule DecentralisedBookIndex.Metadata.BookTest do
       assert alternatives_names = [related_book]
     end
   end
+
+  describe "author's books" do
+    test "get the list via author's id" do
+      {:ok, author} = Metadata.create_author("Author", "An description")
+
+      author_roles = [
+        %{order: 1, author_id: author.id, role: ""}
+      ]
+
+      {:ok, book} = Metadata.create_book("Book", "1234567890", "An description", author_roles)
+
+      assert {:ok, books} = Metadata.get_author_books(author)
+    end
+  end
 end