Mox is ignoring my Mocked module and calling the real function

Did you clear / trigger application rebuilt after introducing the Mox mock? I think I was having similar problem and I had to trigger application recompilation, by either mix clear or even removing the whole _build dir and rebuilding it from scratch.

Hi @hubertlepicki , yes I did but the same result.

I think there is something missing (an implementation or something ?) to detect the mocked function

Hi!
You are missing env variables.
In test_helpers you need to put
Application.put_env(:app_name, :external, MyApp.MockExternalSources)
and in test you need to call it in this way:

Application.get_env(:app_name, :external).fetch_one_external_resource

and mock in test fetch_one_external_resource function instead of http_get_resource.

I suggest that you refactor your MyApp.MyModule.ExternalSources so that http_get_resource methods is implemented in new module.

This way you separate your business logic from contacting external resources.

Hi @karlosmid ,

I have this error :
** (Mox.UnexpectedCallError) no expectation defined for MyApp.MockExternalSources.fetch_one_external_resource/1 in process #PID<0.529.0> with args

Maybe I didn’t get it right, can you please help me add your proposition to my code ?

Mox was expecting fetch_one_external_resource/1 as the name of the function to be called, but your expectation is calling another function.

Yes because I mocked the http_get_resource/2 which does the HTTP call, I just need to simulate that behaviour not the entire fetch_one_external_resource/1 function

Can anyone please show me what’s wrong ?

Here is the updates that I did based on @karlosmid answer.

in test_helper.ex :

I added ;
Application.put_env(:app_name, :external, MyApp.MockExternalSources)

in my test file I updated the assert to :

assert Application.get_env(:app_name, :external).fetch_one_external_resource(params) ==
             %{"new_key1" => "value1", "new_key2" => "value2"}

If I mock fetch_one_external_resource there will not be a real test, It will be a static verification of the result

The core problem is that it’s not enough to create a mock from a behaviour, you should also tell your implementation to use it in tests. Right now, your fetch_one_external_resource is always calling http_get_resource . The implementation is fixed.

As others have already pointed out:

1. Refactor http_get_resource into its own module. Let’s call it “APIClient”
2. Have ExternalSources retrieve which APIClient module to use vie config. By default it would be APIClient, in the test environment it will be APIClientMock
3. Define APIClientMock in thests with defmock and set the desired expectations in your test

Or you could just use Patch

@trisolaran , here is all the updates that I did by I always get an empty left in assertion (left: %{})

In ExternalSources module, I added :

@api_client Application.compile_env!(:app_name, :api_client)

The call to the http_get_resource became :
@api_client.http_get_resource(url, headers)

In test_helper.exs I deleted the lines :

Mox.defmock(MyApp.MockExternalSources, for: MyApp.MyModule.ExternalSources)

and
Application.put_env(:app_name, :external, MyApp.MockExternalSources)

In my test file, I added :

  test "fetch and process external data" do
    Mox.defmock(MyApp.MyModule.APIClientMock,
      for: MyApp.MyModule.APIClient
    )

    MyApp.MyModule.APIClientMock
    |> expect(:http_get_resource, fn _url, _headers ->
      {:ok, %{status_code: 200, body: %{key1: "value1", key2: "value2"}}}
    end)

...

assert MyApp.MyModule.ExternalSources.fetch_one_external_resource(params) ==
             %{"newkey1" => "value1", "newkey2" => "value2"}

In my config.exs :

config :app_name, api_client: MyApp.MyModule.APIClient

In my test.exs :

config :app_name, api_client: MyApp.MyModule.APIClientMock