Add an action to get author's alternatives names.

test/decentralised_book_index/metadata/author_test.exs

@@ -16,7 +16,7 @@ defmodule DecentralisedBookIndex.Metadata.AuthorTest do
     end
 
     test "a new author to a registry via a related author record" do
-      {:ok, related_author}  = Metadata.create_author("Author",  "An description")
+      {:ok, related_author} = Metadata.create_author("Author",  "An description")
 
       assert {:ok, author} =
         Metadata.add_author_to_related_alias_registry("Author2", "An description2", related_author.id)
@@ -29,4 +29,22 @@ defmodule DecentralisedBookIndex.Metadata.AuthorTest do
         Metadata.add_author_to_related_alias_registry("Author2", "An description2", nil)
     end
   end
+
+  describe "authors alternatives names" do
+    test "new author has no alternatives names" do
+      {:ok, author} = Metadata.create_author("Author", "An description")
+      assert {:ok, alternatives_names} = Metadata.get_author_alternative_names(author)
+      assert alternatives_names = []
+    end
+
+    test "author has related author so they has one alternative name" do
+      {:ok, related_author} = Metadata.create_author("Author",  "An description")
+
+      {:ok, author} =
+        Metadata.add_author_to_related_alias_registry("Author2", "An description2", related_author.id)
+
+      assert {:ok, alternatives_names} = Metadata.get_author_alternative_names(author)
+      assert alternatives_names = [related_author]
+    end
+  end
 end