3. Testing the GenServer - abarr/remote GitHub Wiki

Testing a GenServer can be tricky, so I wanted to add a handle_call purely for getting a test working before implementing the next set of requirements.

Setup

I added a the following function to the GenServer

"/lib/remote/users/user_server.ex"

defmodule Remote.Users.UserServer do
  @moduledoc false
  use GenServer
  
  ...
  def get_state(server \\ __MODULE__) do
    GenServer.call(server, {:get_state})
  end
  ...

Then tested it using iex -S mix

$ iex -S mix

Erlang/OTP 24 [erts-12.0] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1]

Compiling 1 file (.ex)
Interactive Elixir (1.13.1) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> Remote.Users.UserServer.get_state()
%{max_number: 31, timestamp: nil}
iex(2)> 

Writing a Test

I added the following test file.

"/test/remote/user_server_test.exs"


defmodule Remote.UserServerTest do
  use ExUnit.Case, async: true

  setup do
    user_server = start_supervised!({Remote.Users.UserServer, name: __MODULE__})
    %{user_server: user_server}
  end

  test "get state", %{user_server: user_server} do
    assert %{max_number: _num, timestamp: nil} = Remote.Users.UserServer.get_state(user_server)
  end
end

Using the start_supervised! option in the setup call back allows me to create a GenServer and pass it to the call to test that the code is working.

Running the tests I see that is working.

$ mix test
...

Finished in 0.03 seconds (0.03s async, 0.00s sync)
3 tests, 0 failures

two of the tests are generated tests for view.