View Source Using Apical for Testing OpenAPI requests

You may use Apical in your test environment to make sure that client requests you perform against a 3rd party OpenAPI server are well-formed.

Often times, tests for API compliance are not performed because they can look like your tests are merely duplicative of the code that you already have. Moreover, if the API changes, then you will have to rewrite all of the tests to remain in compliance with API.

With Apical, you have an easy way of testing that the parameter requirements are fulfilled and that they should not cause 400 or 404 errors when you make the request. You can also use this to test that the parameters you're assigning are correctly bound into the OpenAPI parameters.



In "test" mode, Apical expects that you are using the following two Elixir libraries:

  • Mox to mock out the API controllers.
  • Bypass to stand up transient http servers.



  1. Add dependenciecs:

    In your mix.exs file, add the following dependencies:

       defp deps do
           {:apical, "~> 0.2", only: :test},
           {:mox, "~> 1.0", only: :test},
           {:bypass, "~> 2.1", only: :test},
  2. If you haven't already, set up your elixir compilers to compile to a support directory:

    In mix.exs, project function

       def project do
           elixirc_paths: elixirc_paths(Mix.env()),

    In mix.exs module top level:

       def elixirc_paths(:test), do: ["lib", "test/support"]
       def elixirc_paths(_), do: ["lib"]
  3. Make sure mox and bypass are running when tests are running:

    In test/test_helper.exs:



Router setup

Create a router in your test/support directory.

For example:

defmodule MyAppTest.SomeSAAS do
  use Phoenix.Router

  require Apical

  Apical.router_from_file("path/to/some_saas.yaml", encoding: "application/yaml", testing: :auto)

Note that this macro creates MyAppTest.SomeSAAS.Mock which is the mock for controller serviced by the some_saas OpenAPI schema, as well as the bypass/1,2 function which configures bypass to use the router.

For details on how to set up more fine-grained testing settings, see documentation for Apical module.


Testing module setup

In your test module, start with the following code:

defmodule MyAppTest.SaasRequestTest do
  # tests using Apical in "test" mode where it creates a bypass server.

  use ExUnit.Case, async: true

  alias MyAppTest.SomeSAAS
  alias MyAppTest.SomeSAAS.Mock

  alias MyApp.ClientModule

  setup do
    bypass =
    {:ok, bypass: bypass}

This sets up bypass to serve an http server on its own port for each test run in the test module. Since it's async, the Mox expectations are set up to work with the bypass server.


Testing your API consumer


Required for your API consumer

In order to use this feature, your API consumer functions MUST be able to use a host other than the API's "normal" host.

we'll assume that some ClientModule has

  1. Testing to see that the issued request is compliant (no 400/404 errors)

    In this case, we have function some_operation is compliant and doesn't issue a request to an incorrect path or present invalid parameters.

     test "someOperation" %{bypass: bypass} do
       Mox.expect(Mock, :someOperation, fn conn, _params ->
         send_resp(conn, 200, @dummy_result)
       ClientModule.some_operation(host: "localhost:#{bypass.port}")
  2. Testing to see that parameters are serialized as expected

    This test is an example verification that content issued through a client module into a OpenAPI operation is serialized as expected.


    Scope of parameters

    Keep in mind that parameters can be in cookies, headers, query string, path, or content serialized from the body of the http request parameters taken from the body have lower precedence than taken from the request, if you could potentially have a collision in keys, use the nest_all_json option in your Apical router configuration.

     @test_parameter 47
     test "someOperation" %{bypass: bypass} do
       Mox.expect(Mock, :someOperation, fn conn, %{"parameter-name" => parameter} ->
         assert parameter == @test_parameter
         send_resp(conn, 201, @dummy_result)
       ClientModule.some_operation(@test_parameter, host: "localhost:#{bypass.port}")


    Json Encoding

    note that your client function input parameter might have atom keys (or might be a struct), in which case, strict equality might not be the correct test inside your mox expectation, as Apical will typically render it as a JSON with string keys.