Mock adapter for better testing.

Setup

# config/test.exs
config :tesla, adapter: Tesla.Mock

# in case MyClient defines specific adapter with `adapter SpecificAdapter`
config :tesla, MyClient, adapter: Tesla.Mock

Example test

defmodule MyAppTest do
  use ExUnit.Case

  setup do
    Tesla.Mock.mock(fn
      %{method: :get} ->
        %Tesla.Env{status: 200, body: "hello"}
    end)

    :ok
  end

  test "list things" do
    assert {:ok, env} = MyApp.get("...")
    assert env.status == 200
    assert env.body == "hello"
  end
end

Setting up mocks

# Match on method & url and return whole Tesla.Env
Tesla.Mock.mock(fn
  %{method: :get, url: "http://example.com/list"} ->
    %Tesla.Env{status: 200, body: "hello"}
end)

# You can use any logic required
Tesla.Mock.mock(fn env ->
  case env.url do
    "http://example.com/list" ->
      %Tesla.Env{status: 200, body: "ok!"}

    _ ->
      %Tesla.Env{status: 404, body: "NotFound"}
  end
end)


# mock will also accept short version of response
# in the form of {status, headers, body}
Tesla.Mock.mock(fn
  %{method: :post} -> {201, %{}, %{id: 42}}
end)

Global mocks

By default, mocks are bound to the current process, i.e. the process running a single test case. This design allows proper isolation between test cases and make testing in parallel (async: true) possible.

While this style is recommended, there is one drawback: if Tesla client is called from different process it will not use the setup mock.

To solve this issue it is possible to setup a global mock using mock_global/1 function.

defmodule MyTest do
  use ExUnit.Case, async: false # must be false!

  setup_all do
    Tesla.Mock.mock_global fn
      env -> # ...
    end

    :ok
  end

  # ...
end

WARNING: Using global mocks may affect tests with local mock (because of fallback to global mock in case local one is not found)