add limit of post per day

spec/models/post_spec.rb

@@ -28,4 +28,30 @@ RSpec.describe Post, type: :model do
       end
     end
   end
+
+  describe '#limit_of_post_per_day' do
+    context 'when user tries to post more than 5 times in a day' do
+      it 'returns error' do
+        user = create(:user)
+
+        5.times do
+          create(:post, user: user)
+        end
+
+        expect(build(:post, user: user).valid?).to be_falsey
+      end
+    end
+
+    context 'when the user has not yet reached their publication limit' do
+      it 'does not returns error' do
+        user = create(:user)
+
+        4.times do
+          create(:post, user: user)
+        end
+
+        expect(build(:post, user: user).valid?).to be_truthy
+      end
+    end
+  end
 end