How to test JSON result from Ruby on Rails functional tests?

Question

How can I assert my Ajax request and test the JSON output from Ruby on Rails functional tests?

Answer 1

You can use the AssertJson gem for a nice DSL which allows you to check for keys and values which should exist in your JSON response.

Add the gem to your Gemfile:

group :test do
  gem 'assert_json'
end

This is a quick example how your functional/controller test could look like (the example is an adaption from their README):

class ExampleControllerTest < ActionController::TestCase
  include AssertJson

  def test_my_action
    get :my_action, :format => 'json'
    # => @response.body= '{"key":[{"inner_key":"value1"}]}'

    assert_json(@response.body) do
      has 'key' do
        has 'inner_key', 'value1'
      end
      has_not 'key_not_included'
    end
  end

end

You just have to include the AssertJson module in your test and use the assert_json block where you can check the response for existent and non-existant keys and values. Hint: it's not immediately visible in the README, but to check for a value (e.g. if your action just returns an array of strings) you can do

  def test_my_action
    get :my_action, :format => 'json'
    # => @response.body= '["value1", "value2"]'

    assert_json(@response.body) do
      has 'value1'
      has 'value2'
      has_not 'value3'
    end
  end