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

If you are using RSpec, json_spec is worth a look

https://github.com/collectiveidea/json_spec

Answer 2

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

Answer 3

As noted, you use JSON.parse to test the JSON, but where you perform that assertion depends on how you are rendering the JSON.

If you are generating the JSON in the controller, you parse the JSON in controller functional tests (as the other answers are showing). If you are rendering JSON, with a view using Jbuilder, rabl or another gem that takes this approach, then parse the JSON in the view unit tests not the controller functional tests. Unit tests are generally faster to execute and easier to write - e.g., you can build models in-memory rather than create them in the database.

Answer 4

Actually, you can use implicitly the JSON module:

assert_equal assigns(:user).to_json, @response.body

Answer 5

In Rails >= 5

Use ActionDispatch::TestResponse#parsed_body.

Example:

user = @response.parsed_body
assert_equal "Mike", user['name']

In Rails up to 4.x

Use JSON.parse, which takes a string as input and returns a Ruby hash that the JSON represents.

Example:

user = JSON.parse(@response.body)
assert_equal "Mike", user['name']

Answer 6

Also for short JSON responses you can simply match a string of the JSON to @response.body. This prevents having to rely on yet another gem.

assert_equal '{"total_votes":1}', @response.body