improve mention model test coverage (#20652)

spec/models/mention_spec.rb

@@ -1,9 +1,9 @@
 require "rails_helper"
 
 RSpec.describe Mention do
-  let(:comment) { create(:comment, commentable: create(:podcast_episode)) }
+  describe ".create_all" do
+    let(:comment) { create(:comment, commentable: create(:podcast_episode)) }
 
-  describe "#create_all" do
     it "enqueues a job to default queue" do
       expect do
         described_class.create_all(comment)
@@ -11,13 +11,51 @@ RSpec.describe Mention do
     end
   end
 
-  # TODO: Replace this test with validation spec
-  it "creates a valid mention" do
-    expect(create(:mention)).to be_valid
+  describe "validations" do
+    it { is_expected.to validate_presence_of(:mentionable_type) }
+
+    context "when validating uniqueness of user_id" do
+      let(:user) { create(:user) }
+      let(:mention) { create(:mention, user: user) }
+
+      it "is scoped to mentionable_id and mentionable_type" do
+        duplicate_mention = build(:mention, user: user, mentionable: mention.mentionable)
+
+        expect(duplicate_mention).not_to be_valid
+      end
+
+      it "allows the same user_id for different mentionable_id and mentionable_type" do
+        other_mention = build(:mention, user: user)
+
+        expect(other_mention).to be_valid
+      end
+    end
+
+    context "when mentionable is invalid" do
+      let(:comment) { build(:comment, commentable: nil) }
+
+      it "is invalid" do
+        mention = build(:mention, mentionable: comment)
+
+        expect(mention).not_to be_valid
+      end
+    end
   end
 
-  # TODO: Replace this test with validation spec
-  it "doesn't raise undefined method for NilClass on valid?" do
-    expect(described_class.new.valid?).to be(false)
+  describe "associations" do
+    it { is_expected.to belong_to(:user) }
+    it { is_expected.to belong_to(:mentionable) }
+  end
+
+  describe "callbacks" do
+    let(:mention) { build(:mention) }
+
+    it "enqueues SendEmailNotificationWorker after create" do
+      allow(Mentions::SendEmailNotificationWorker).to receive(:perform_async)
+
+      mention.save
+
+      expect(Mentions::SendEmailNotificationWorker).to have_received(:perform_async).with(mention.id)
+    end
   end
 end