devonestes

# Step 1

def create_subscription(email, plan_id, payment_method_id) do
  with %User{customer_id: nil, name: name} = user <-
         Repo.get_by(User, email: email),
       {:ok, %Stripe.Customer{id: customer_id}} <-
         Stripe.Customer.create(%{
           name: name,
           email: email,
           payment_method: payment_method_id,

devonestes

defmodule Mix.Tasks.Credo.Ci do
  @shortdoc "Run Credo only on files that have changed since the last merge commit."

  @moduledoc """
  Runs Credo in CI with somewhat special behavior.

  If the branch being tested is `master`, it runs Credo on all files. Otherwise, it only runs
  Credo on the files that have changed since the last merge commit, and it will fail CI if any
  check doesn't pass for those specific files.
  """

devonestes

# Given that we have a `User` module, that looks something like this:

defmodule User do
  defstruct [:name]
  
  def changeset(user, params) do
    # ...
  end
end

devonestes

Muzak

What is Muzak?

Muzak is a mutation testing library for Elixir and Erlang applications.

What is Mutation Testing?

Mutation testing is a way of systematically introducing bugs into your code and then running your tests to see if any of them fail. If you introduce a bug in your code

devonestes

# My GenServer

defmodule My.GenServer do
  def start_link() do
    GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
  end

  def init(_) do
    {:ok, []}
  end

devonestes

def intermittent_failures(
      %{id: suite_id},
      spec \\ %{10 => 100, 9 => 80, 8 => 60, 7 => 45, 6 => 32, 5 => 25, 4 => 16, 3 => 9}
    ) do
  limit = spec |> Map.values() |> Enum.max()

  last_100_runs =
    from(r in Run,
      where: r.suite_id == ^suite_id,
      order_by: [desc: r.inserted_at],

devonestes

for num <- [1, 2, 3], num < 3, do: num * 2

devonestes

#!/usr/bin/env escript
%% -*- erlang -*-
%%! -smp enable -sname wtf
main(_) ->
    process_flag(trap_exit, true),
    ToMap = lists:seq(1, 50),
    MapFun = fun() ->
               lists:map(fun(N) -> N end, ToMap)
             end,
    start_runner(MapFun),

devonestes

defmodule SendAfter do
  def send_after(pid, message, nanoseconds) do
    {_, os_name} = :os.type()
    increment =
      if os_name == :Windows do
        # monotonic time for Windows in miliseconds, in Linux and MacOS it's nanoseconds
        # so we'll need to convert to miliseconds for windows
        nanoseconds / 1_000_000
      else
        nanoseconds

devonestes

import Header from './header.jsx';

function headerFun(input) {
  <h1>{input.name}</h1>
}

function DesktopHeader(input) {
  <Header {...{input, headerFun}} />
}