CHIP 7.9: Using BDD to Drive a New Feature

In a previous assignment, you practiced creating Cucumber steps and step definitions to test an existing app, as a way of getting practice with how Cucumber acceptance tests work.

But in real BDD, it is the other way around--you write the Cucumber scenarios and steps before the app, watch the steps fail, and then add code to make one step at a time pass. That is, the behavior described in the steps should drive the development of the code that implements that behavior. Importantly, the Cucumber steps only describe what the observed behavior should be, rarely saying anything about how the behavior is implemented.

In this assignment you will start from Cucumber scenarios that fail because they are trying to acceptance-test features that haven't been implemented yet, and one step at a time, you will write the code that makes those steps pass. The idea is that we are adding a "find movies with same director" feature to RottenPotatoes, and these new scenarios are supposed to test that feature.

Learning Goals

After you complete this assignment, you should be able to:

• Create and run simple Cucumber scenarios to test a new feature
• Understand where to modify a Rails app to implement the various parts of a new feature, since a new feature often touches the database schema, model(s), view(s), and controller(s)
• Use the failing scenario step to drive those modifications and ultimately make the Cucumber scenarios pass, thereby validating the high-level behavior of the new feature

Get the assignment code

Create a copy of the repository on your GitHub account.

We recommend you name your repo hw-bdd-new-feature. Remember to mark the repository as Private.

Then clone the repo to Codio:

git clone [email protected]:[your_github_username]/hw-bdd-new-feature.git

(You can also go to your github repo for this assignment and click the green code button and copy the url. Then type git clone in codio terminal and paste the url and add rottenpotatoes after it.)

⚠️ Your directory must be named hw-bdd-new-feature.

You can also explore the repo on GitHub.

📌 Tip: Use git tags

We recommend that you make a commit as soon as you get each part working.

As an optional additional help, git allows you to associate tags--symbolic names--with particular commits. For example, immediately after doing a commit, you could run git tag part1b, and thereafter you could use git diff part1b to see differences since that commit, rather than remembering its commit ID. Note that after creating a tag in your local repo, you need to use git push origin --tags to push the tags to your remote. (Tags are ignored by deployment remotes such as Heroku, so there's no point in pushing tags there.)

Note: Publishing your homework to a public repo is against the Honor Code.

Run and Prep rottenpotatoes

Once you have the clone of the repo:

1. Change into the rottenpotatoes directory: cd hw-bdd-new-feature

2. Run bundle install --without production to make sure all gems are properly installed.

   NOTE: If Bundler complains that the wrong Ruby version is installed, verify that rvm is installed (for example, rvm --version) and say rvm list to see which Ruby versions are available and rvm use version to make a particular version active. If no versions satisfying the Gemfile dependency are installed, you can say rvm install version to install a new version, then rvm use version to use it. Then you can try bundle install again.

3. Create the initial database schema:

bundle exec rails db:migrate
bundle exec rails db:test:prepare

4. You can optionally add some seed data in db/seeds.rb and run rails db:seed to add it.

5. Double check that Cucumber is correctly set up by running cucumber. We've provided a couple of scenarios that will fail, which you can use as a starting point, in features/movies_by_director.feature.

What is the first failure Cucumber reports? Reading the error message carefully, what is the cause of this specific failure, and what should you modify to make progress? HINT: Start reading at the beginning of the trace and look for the first place where you see an actual error string, rather than a warning or informational log message. Cucumber even prints these in red. Take note of what part of the system the error is coming from (a file in your app? a part of Rails? etc.)

The Cucumber test is trying to load some movie data into the test database including a movie director, but the existing definition of a movie doesn't have a director field. You need to create and apply a migration to add this attribute.

Go on to the next part to modify your app to get past this error.