I’m finishing reading Dave Thomas’s book “Programming Elixir 1.6”. And I was faced with a question about how to test terminate callback from GenServer. I made a test for this, but I’m not sure that it’s a good practice to test in the way that I did. Also, I didn’t find an answer on how to test terminate on google and this forum.
Here is an example of how my GenServer looks like.
defmodule Sequence.Server do
use GenServer
@me __MODULE__
#####
# External API
def init(_) do
{:ok, Sequence.Stash.get()}
end
def start_link(_) do
GenServer.start_link(@me, nil, name: @me)
end
def current_number do
GenServer.call(@me, :current_number)
end
def next_number do
GenServer.call(@me, :next_number)
end
def update_number(new_number) when is_integer(new_number) do
GenServer.cast(@me, {:update, new_number})
end
def increment_number(delta) do
GenServer.cast(@me, {:increment_number, delta})
end
#####
# GenServer implementation
def handle_call(:next_number, _from, current_number) do
{:reply, current_number, current_number + 1}
end
def handle_call(:current_number, _from, current_number) do
{:reply, current_number, current_number}
end
def handle_cast({:increment_number, delta}, current_number) do
{:noreply, current_number + delta}
end
def handle_cast({:update, new_number}, _current_number) do
{:noreply, new_number}
end
def terminate(_reason, current_number) do
Sequence.Stash.update(current_number)
end
def format_status(_reason, [_pdict, state]) do
[data: [{'State', "My current state is '#{inspect(state)}'"}]]
end
end
And here is an example of how I tried to test this callback.
defmodule ServerTest do
use ExUnit.Case
alias Sequence.Server
import :timer, only: [ sleep: 1 ]
setup do
Server.update_number(1)
end
test "terminate returns last value before terminating" do
assert Server.next_number == 1
Server.increment_number("cat")
sleep(500)
assert Server.current_number == 2
end
end