Example of mocking a web api in ExUnit in Elixir using Meck

test.exs

# https://github.com/eproxus/meck
# add meck as a dependency in mix.exs

defmodule GithubIssuesTest do
  use ExUnit.Case
  import :meck

  setup_all do
    new(Issues.GithubIssues)
    on_exit fn -> unload end
    :ok
  end

  test "successful fetch with user and a project" do
    # already decoded from raw json using jsx in pipeline
    mock_response = {:ok, [
      [
        {"url", "https://api.github.com/repos/elixir-lang/elixir/issues/2956"},
        {"html_url", "https://github.com/elixir-lang/elixir/issues/2956"},
        {"id", 52467010},
        {"number", 2956}
        ]
      ]
    }

    # use meck to create a mock response
    expect(Issues.GithubIssues, :fetch, fn("elixir-lang", "elixir") -> mock_response end)

    # calls the actual function which makes the actual api call!
    # expect(Issues.GithubIssues, :fetch, fn("elixir-lang", "elixir") -> :meck.passthrough(["elixir-lang", "elixir"]) end)


    assert validate(Issues.GithubIssues)

    assert Issues.GithubIssues.fetch("elixir-lang", "elixir") == mock_response
  end
end