How to test a JSON API?

Any language with a decent HTTP library and a JSON library ought to do. Just pick your favorite language and testing framework and go for it. I'd probably use RSpec and Rack::Test, especially if the API will be implemented in Ruby, but tastes vary.

Edit: You mentioned you'd like to run the tests outside the server. If you're sure about that then use e.g. Net::HTTP instead of Rack::Test.

Usually API is regular controllers/actions. So you can test this actions as regular controller inside of server app. Thats like i test my API actions:

describe Api::AccountsController do
  describe "GET :index" do
    it "should be success" do
      do_get
      response.should be_success
    end

    it "should return list of accounts" do
      5.times{ Factory :account }
      do_get
      JSON.parse(response.body).size.should == 5
    end

    it "should return id, name and description of each account" do
      account = Factory :account
      do_get
      result = JSON.parse(response.body).first
      result['account']['id'].should == account.id
      result['account']['name'].should == account.name
      result['account']['description'].should == account.description
    end

    def do_get
      get :index, :format => :json
    end
  end
end

I've worked on a JS API for Rails and built a whole set of tests using QUnit and jQuery. I was quite happy with the end result, my aim was to test the API thoroughly and this combination of tools was everything I needed.

I've been working on a new project that uses Jasmine, its a bit more descriptive in the way you write tests (which makes the Business Analysts happy) but the end result was much the same as QUnit.

It seems like some have found success with cucumber (checkout this similar question)

What is the recommended method of testing a JSON client-server api?

I agree with @mpartel completely.

You'll presumably want a set of unit tests (without the complexity of HTTP) to test the logic of your implementation. Once you go down that route, you'll find that there will be a benefit in writing the tests in the same language.

For example, you if you write it in Rails (and use Rack::Test), you'll also be able to unit test lots of the cases in a simpler Test::Unit (or RSpec) environment.

One way you can do this is controller tests using rspec

describe PersonApiController 
  # GET /person/1.json
  it "should respond with a person" do 
     person = Person.create(:name => "scott")
     get :show, :id => person.id, :format => 'json'
     response.should be_success
     response.body.should have_selector('name', :content => person.name)
  end
end 

If you want to get even fancier, you can share a api client via a plugin/gem between your client code and your server code and then initialize it using the json like

person_client = PersonClient.new(response.body)
person_client.name.should eql 'scott'

Just write some specs with Cucumber and/or RSpec to connect to your app and test the output. No need to drag JQuery into it.

http://www.soapui.org/

a functional testing tool.

I did it! This is how to do it with vanilla Rails. Notice the different accept mime type. You may parse the JSON if you wish. Comparing as strings was sufficient.

  test "vote comment up" do
    # @request.headers["Content-Type"] = "application/json"
    @request.headers["Accept"] = "application/javascript"
    post :up, {post_id: 1, id: 1}, {user_id: 5}
    assert_response :success
    assert_equal @response.body, '{"error":true,"errorPath":"/users/5/balance","userVotes":1,"totalVotes":0}'
  end

If you want to test during development, I use Advanced Rest Client Chrome Extension.