Add cop for has_one as well

config/default.yml

@@ -1,6 +1,6 @@
 # Write it!
 
-Teamtailor/NoHasManyInActiveModelSerializer:
+Teamtailor/NoEmbeddingsInActiveModelSerializer:
   Description: "TODO: Write a description of the cop."
   Enabled: true
   VersionAdded: "<<next>>"

lib/rubocop/cop/teamtailor/no_has_many_in_active_model_serializer.rb → lib/rubocop/cop/teamtailor/no_embeddings_in_active_model_serializer.rb

@@ -3,11 +3,11 @@
 module RuboCop
   module Cop
     module Teamtailor
-      class NoHasManyInActiveModelSerializer < Base
+      class NoEmbeddingsInActiveModelSerializer < Base
         MSG = "No embedding of records"
 
         def_node_matcher :no_has_many?, <<~PATTERN
-          (send nil? :has_many ...)
+          (send nil? {:has_many | :has_one} ...)
         PATTERN
 
         def on_class(class_node)

lib/rubocop/cop/teamtailor_cops.rb

@@ -1,3 +1,3 @@
 # frozen_string_literal: true
 
-require_relative "teamtailor/no_has_many_in_active_model_serializer"
+require_relative "teamtailor/no_embeddings_in_active_model_serializer"

spec/rubocop/cop/teamtailor/no_embeddings_in_active_model_serializer_spec.rb

@@ -0,0 +1,66 @@
+# frozen_string_literal: true
+
+RSpec.describe RuboCop::Cop::Teamtailor::NoEmbeddingsInActiveModelSerializer, :config do
+  let(:config) { RuboCop::Config.new }
+
+  context "when in a serializer" do
+    it "registers an offense when using `has_many`" do
+      expect_offense(<<~RUBY)
+        class FooSerializer < ActiveModel::Serializer
+          has_many :locations, embed: :ids
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Teamtailor/NoEmbeddingsInActiveModelSerializer: No embedding of records
+        end
+      RUBY
+    end
+
+    it "registers an offense when using `has_one`" do
+      expect_offense(<<~RUBY)
+        class FooSerializer < ActiveModel::Serializer
+          has_one :location, embed_in_root: true
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Teamtailor/NoEmbeddingsInActiveModelSerializer: No embedding of records
+        end
+      RUBY
+    end
+
+    it "registers offenses for all `has_many`" do
+      expect_offense(<<~RUBY)
+        class FooSerializer < ActiveModel::Serializer
+          has_many :locations, embed: :ids
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Teamtailor/NoEmbeddingsInActiveModelSerializer: No embedding of records
+          has_many :users, embed: :ids
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Teamtailor/NoEmbeddingsInActiveModelSerializer: No embedding of records
+        end
+      RUBY
+    end
+
+    it "registers offenses for both `has_many` and `has_one`" do
+      expect_offense(<<~RUBY)
+        class FooSerializer < ActiveModel::Serializer
+          has_many :locations, embed: :ids
+          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Teamtailor/NoEmbeddingsInActiveModelSerializer: No embedding of records
+          has_one :user, embed: :id
+          ^^^^^^^^^^^^^^^^^^^^^^^^^ Teamtailor/NoEmbeddingsInActiveModelSerializer: No embedding of records
+        end
+      RUBY
+    end
+
+    it "does not register an offence when no has_one/has_many" do
+      expect_no_offenses(<<~RUBY)
+        class FooSerializer < ActiveModel::Serializer
+          attributes :location_ids
+        end
+      RUBY
+    end
+  end
+
+  context "when not in a serializer" do
+    it "does not register an offense when using has_many" do
+      expect_no_offenses(<<~RUBY)
+        class Foo
+          has_many :locations
+          has_one :user
+        end
+      RUBY
+    end
+  end
+end