添加gem 'rails-controller-testing'后Rails测试仍报assert_template错误

Hey, I’ve dealt with this exact problem on Rails teams before—let’s break down why this happens and walk through the fixes:

Core Background #

First, a quick recap: assert_template was pulled out of Rails core starting in Rails 5, so you must have the rails-controller-testing gem installed to use it. Your local setup works because you added the gem, but your teammate’s machine is still missing it for one of these common reasons:

1. You Forgot to Commit the Gemfile/Gemfile.lock Changes #

Double-check that you actually pushed the gem addition to Git:

• Run git status locally to see if Gemfile and Gemfile.lock are tracked and committed.
• If they’re not, fix it with these commands:

  git add Gemfile Gemfile.lock
  git commit -m "Add rails-controller-testing gem to support assert_template"
  git push
  

  Then have your teammate run git pull again to get the updated files.

2. Your Teammate Didn’t Run bundle install After Pulling #

It’s easy to forget this step! Tell them to run this in the project root:

bundle install

If they use a local gem path (with bundle install --path vendor/bundle), they might need to clean old dependencies first:

bundle clean --force
bundle install

3. There’s a Conflict in Gemfile.lock #

If multiple people edited the Gemfile around the same time, Git might have created a conflict in Gemfile.lock. Have your teammate:

1. Resolve the conflict in Gemfile.lock (keep the version of rails-controller-testing you added)
2. Run bundle install to regenerate a clean Gemfile.lock
3. Commit the resolved file and push if needed

4. The Gem Is in the Wrong Group in Gemfile #

Make sure rails-controller-testing is in the :test group in your Gemfile—otherwise, it won’t load in the test environment. Your Gemfile should look like this:

group :test do
  gem 'rails-controller-testing'
  # Other test gems like rspec-rails, capybara, etc.
end

If it’s outside the :test group, move it and re-run bundle install, then commit/push the updated files.

5. Their IDE/Test Runner Is Caching Dependencies #

Sometimes IDEs (like VS Code or RubyMine) cache gem environments. Have them restart their IDE or reload the project’s gem setup to ensure the new gem is recognized.

Pro tip: Always commit both Gemfile and Gemfile.lock when adding/updating gems—this ensures everyone on the team gets the exact same dependency versions, avoiding "works on my machine" headaches.

内容的提问来源于stack exchange，提问作者Jacob Lockard