gitlab-org--gitlab-foss/doc/development/testing_guide/contract/provider_tests.md

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# Writing provider tests

This tutorial guides you through writing a provider test from scratch. It is a continuation of the [consumer test tutorial](consumer_tests.md). To start, the provider tests are written using [`pact-ruby`](https://github.com/pact-foundation/pact-ruby). In this tutorial, you write a provider test that addresses the contract generated by `discussions.spec.js`.

## Create the skeleton

Provider tests are quite simple. The goal is to set up the test data and then link that with the corresponding contract. Start by creating a file called `discussions_helper.rb` under `spec/contracts/provider/specs`. Note that the files are called `helpers` to match how they are called by Pact in the Rake tasks, which are set up at the end of this tutorial.

### The `service_provider` block

The `service_provider` block is where the provider test is defined. For this block, put in a description of the service provider. Name it exactly as it is called in the contracts that are derived from the consumer tests.

```ruby
require_relative '../spec_helper'

module Provider
  module DiscussionsHelper
    Pact.service_provider 'Merge Request Discussions Endpoint' do
      
    end
  end
end
```

### The `honours_pact_with` block

The `honours_pact_with` block describes which consumer this provider test is addressing. Similar to the `service_provider` block, name this exactly the same as it's called in the contracts that are derived from the consumer tests.

```ruby
require_relative '../spec_helper'

module Provider
  module DiscussionsHelper
    Pact.service_provider 'Merge Request Discussions Endpoint' do
      honours_pact_with 'Merge Request Page' do
        
      end
    end
  end
end
```

## Configure the test app

For the provider tests to verify the contracts, you must hook it up to a test app that makes the actual request and return a response to verify against the contract. To do this, configure the `app` the test uses as `Environment::Test.app`, which is defined in [`spec/contracts/provider/environments/test.rb`](https://gitlab.com/gitlab-org/gitlab/-/tree/master/spec/contracts/provider/environments/test.rb).

```ruby
require_relative '../spec_helper'

module Provider
  module DiscussionsHelper
    Pact.service_provider 'Merge Request Discussions Endpoint' do
      app { Environment::Test.app }
      
      honours_pact_with 'Merge Request Page' do
        
      end
    end
  end
end
```

## Define the contract to verify

Now that the test app is configured, all that is left is to define which contract this provider test is verifying. To do this, set the `pact_uri`.

```ruby
require_relative '../spec_helper'

module Provider
  module DiscussionsHelper
    Pact.service_provider 'Merge Request Discussions Endpoint' do
      app { Environment::Test.app }
      
      honours_pact_with 'Merge Request Page' do
        pact_uri '../contracts/merge_request_page-merge_request_discussions_endpoint.json'
      end
    end
  end
end
```

## Add / update the Rake tasks

Now that you have a test created, you must create Rake tasks that run this test. The Rake tasks are defined in [`lib/tasks/contracts.rake`](https://gitlab.com/gitlab-org/gitlab/-/tree/master/lib/tasks/contracts.rake) where we have individual Rake tasks to run individual specs, but also Rake tasks that run a group of tests.

Under the `contracts:mr` namespace, introduce the Rake task to run this new test specifically. In it, call `pact.uri` to define the location of the contract and the provider test that tests that contract. Notice here that `pact_uri` has a parameter called `pact_helper`. This is why the provider tests are called `_helper.rb`.

```ruby
Pact::VerificationTask.new(:discussions) do |pact|
  pact.uri(
    "#{contracts}/contracts/merge_request_page-merge_request_discussions_endpoint.json",
    pact_helper: "#{provider}/specs/discussions_helper.rb"
  )
end
```

At the same time, add your new `:discussions` Rake task to be included in the `test:merge_request` Rake task. In that Rake task, there is an array defined (`%w[metadata diffs]`). You must add `discussions` in that list.

## Create test data

As the last step, create the test data that allows the provider test to return the contract's expected response. You might wonder why you create the test data last. It's really a matter of preference. With the test already configured, you can easily run the test to verify and make sure all the necessary test data are created to produce the expected response.

You can read more about [provider states](https://docs.pact.io/implementation_guides/ruby/provider_states). We can do global provider states but for this tutorial, the provider state is for one specific `state`.

To create the test data, create `discussions_state.rb` under `spec/contracts/provider/states`. As a quick aside, make sure to also import this state file in the `discussions_helper.rb` file.

### Default user in `spec/contracts/provider/spec_helper.rb`

Before you create the test data, note that a default user is created in the [`spec_helper`](https://gitlab.com/gitlab-org/gitlab/-/tree/master/spec/contracts/provider/spec_helper.rb), which is the user being used for the test runs. This user is configured using `RSpec.configure`, as Pact actually is built on top of RSpec. This step allows us to configure the user before any of the test runs.

```ruby
RSpec.configure do |config|
  config.include Devise::Test::IntegrationHelpers
  config.before do
    user = FactoryBot.create(:user, name: "Contract Test").tap do |user|
      user.current_sign_in_at = Time.current
    end
    sign_in user
  end
end
```

Any further modifications to the user that's needed can be done through the individual provider state files.

### The `provider_states_for` block

In the state file, you must define which consumer this provider state is for. You can do that with `provider_states_for`. Make sure that the `name` provided matches the name defined for the consumer.

```ruby
Pact.provider_states_for 'Merge Request Page' do
end
```

### The `provider_state` block

In the `provider_states_for` block, you then define the state the test data is for. These states are also defined in the consumer test. In this case, there is a `'a merge request with discussions exists'` state.

```ruby
Pact.provider_states_for "Merge Request Page" do
  provider_state "a merge request with discussions exists" do

  end
end
```

### The `set_up` block

This is where you define the test data creation steps. Use `FactoryBot` to create the data. As you create the test data, you can keep [running the provider test](index.md#run-the-provider-tests) to check on the status of the test and figure out what else is missing in your data setup.

```ruby
Pact.provider_states_for "Merge Request Page" do
  provider_state "a merge request with discussions exists" do
    set_up do
      user = User.find_by(name: Provider::UsersHelper::CONTRACT_USER_NAME)
      namespace = create(:namespace, name: 'gitlab-org')
      project = create(:project, name: 'gitlab-qa', namespace: namespace)

      project.add_maintainer(user)

      merge_request = create(:merge_request_with_diffs, id: 1, source_project: project, author: user)

      create(:discussion_note_on_merge_request, noteable: merge_request, project: project, author: user)
    end
  end
end
```

Note the `Provider::UsersHelper::CONTRACT_USER_NAME` here to fetch a user is a user that is from the [`spec_helper`](https://gitlab.com/gitlab-org/gitlab/-/tree/master/spec/contracts/provider/spec_helper.rb) that sets up a user before any of these tests run.

And with that, the provider tests for `discussion_helper.rb` should now pass with this.