When working with third-party APIs like the weather API, we push the code that integrates with the API outside our application in a lightweight wrapper. When we’re testing our application, we’re able to swap out that small part with a double to run the rest of our application. However, we also need to make sure that the code that interacts with the API works. We’ll need a test for that.

In our weather API application, the code that interacts with the weather API is this:

defmodule SoggyWaffle.WeatherAPI do
  @behaviour SoggyWaffle.WeatherAPI.Behaviour
  @spec get_forecast(String.t()) ::
          {:ok, map()} | {:error, reason :: term()}
  def get_forecast(city) when is_binary(city) do
    app_id = SoggyWaffle.api_key()
    query_params = URI.encode_query(%{"q" => city, "APPID" => app_id})
    url =
      "https://api.openweathermap.org/data/2.5/forecast?" <> query_params
    case HTTPoison.get(url) do
      {:ok, %HTTPoison.Response{status_code: 200} = response} ->
        {:ok, Jason.decode!(response.body)}
      {:ok, %HTTPoison.Response{status_code: status_code}} ->
        {:error, {:status, status_code}}
      {:error, reason} ->
        {:error, reason}
    end
  end
end

Unit Tests

Integration and End-to-End Tests

Testing OTP

Testing Ecto Schemas

Testing Ecto Queries

Testing Phoenix

Property-Based Testing

Conclusion

Testing the Actual Interaction with Services