Update spec with included documents with no explicitly given fields

spec/lib/object_serializer_fields_spec.rb

@@ -5,7 +5,7 @@ describe FastJsonapi::ObjectSerializer do
 
   let(:fields) do
     {
-      movie: %i[name actors],
+      movie: %i[name actors advertising_campaign],
       actor: %i[name agency]
     }
   end
@@ -19,7 +19,7 @@ describe FastJsonapi::ObjectSerializer do
   it 'only returns specified relationships' do
     hash = MovieSerializer.new(movie, fields: fields).serializable_hash
 
-    expect(hash[:data][:relationships].keys.sort).to eq %i[actors]
+    expect(hash[:data][:relationships].keys.sort).to eq %i[actors advertising_campaign]
   end
 
   it 'only returns specified fields for included relationships' do
@@ -29,8 +29,20 @@ describe FastJsonapi::ObjectSerializer do
   end
 
   it 'only returns specified relationships for included relationships' do
-    hash = MovieSerializer.new(movie, fields: fields, include: %i[actors]).serializable_hash
+    hash = MovieSerializer.new(movie, fields: fields, include: %i[actors advertising_campaign]).serializable_hash
 
     expect(hash[:included].first[:relationships].keys.sort).to eq %i[agency]
   end
+
+  it 'returns all fields for included relationships when no explicit fields have been specified' do
+    hash = MovieSerializer.new(movie, fields: fields, include: %i[actors advertising_campaign]).serializable_hash
+
+    expect(hash[:included][3][:attributes].keys.sort).to eq %i[id name]
+  end
+
+  it 'returns all fields for included relationships when no explicit fields have been specified' do
+    hash = MovieSerializer.new(movie, fields: fields, include: %i[actors advertising_campaign]).serializable_hash
+
+    expect(hash[:included][3][:relationships].keys.sort).to eq %i[movie]
+  end
 end