ExZample
A scalable error-friendly factories library for your Elixir apps
Installation
If available in Hex, the package can be installed
by adding ex_zample
to your list of dependencies in mix.exs
:
def deps do
[
{:ex_zample, "~> 0.6.0"}
]
end
Documentation can be generated with ExDoc and published on HexDocs. Once published, the docs can be found at https://hexdocs.pm/ex_zample.
Quick Start
You can build any struct by passing a struct module:
ExZample.build(User)
# => %MyApp.User{first_name: nil, age: 21}
ExZample
will automatically use the default values inside of that struct. If
you want to define different values, you can create factories using
ExZample.DSL
. For example:
defmodule MyApp.Factories do
use ExZample.DSL
alias ExZample.User
factory :user do
example do
%User{
first_name: "Abili De Bob",
age: 12,
}
end
end
end
# Don't forget to start :ex_zample app!
# for example, in your: test_helper.exs
:ok = Application.ensure_started(:ex_zample)
Now you can invoke them like this:
ExZample.build(:user)
# => %MyApp.User{first_name: "Abili De Bob", age: 12}
This is the basics of what you need to start using ExZample
. The later section
of this README we'll dig in details of how this library works.
Building your factories
You can use the build/2
, build_pair/2
and build_list/3
to generate data
without side-effects.
# or using aliases
ExZample.build(:user, age: 42)
# => %MyApp.User{first_name: "Abili De Bob", age: 42}
ExZample.build_pair(:user, age: 42)
# => {%MyApp.User{first_name: "Abili De Bob", age: 42}, %MyApp.User{first_name: "Abili De Bob", age: 42}}
ExZample.build_list(100, :user, age: 42)
# => [
# %MyApp.User{first_name: "Abili De Bob", age: 42},
# %MyApp.User{first_name: "Abili De Bob", age: 42},
# ...
# ]
# or using the modules directly
ExZample.build(UserFactory, age: 42)
# => %MyApp.User{first_name: "Abili De Bob", age: 42}
ExZample.build_pair(UserFactory, age: 42)
# => {%MyApp.User{first_name: "Abili De Bob", age: 42}, %MyApp.User{first_name: "Abili De Bob", age: 42}}
ExZample.build_list(100, UserFactory, age: 42)
# => [
# %MyApp.User{first_name: "Abili De Bob", age: 42},
# %MyApp.User{first_name: "Abili De Bob", age: 42},
# ...
# ]
When you pass attributes, it will override the default ones defined in your factories.
Sequences
Sequences are global counters that you can user in your tests. When your test suite starts you can create sequences using ExZample.create_sequence
. For example,
in your test_helper.exs
:
# test_helper.exs
:ok = Application.ensure_started(:ex_zample)
ExZample.create_sequence(:order_id)
ExZample.create_sequence(:user_email, &"email_#{&1}@test.test")
Then, in your factories or in your tests you can invoke them using
ExZample.sequence/1
this:
factory :user do
example do
%User{
email: sequence(:user_email),
name: "Abili de bob"
}
end
end
# or in your tests
test "tracks an order" do
order_id = ExZample.sequence(:order_id)
# => 1
end
Sequences are Agent
processes, no matter how many processes tries to get the
next value, the OTP will guarantee it will always generate a different one for
each request.
ExZample and Umbrella apps
If you want to avoid the factories or sequences leaking through different apps in your umbrella, you can define them under a scope.
# defining factories
defmodule MyApp.Factories do
use ExZample.DSL, scope: :app_a
alias ExZample.User
factory :user do
example do
%User{
first_name: "Abili De Bob",
age: 12,
}
end
end
end
# in apps/myapp_a/test/test_helper.ex
ExZample.create_sequence(:app_a, :user_email, &"user_#{&1}@test.test")
Then, you can use ExZample.ex_zample/1
to narrow the scope of lookups
during in your tests. It fits well with ExUnit @tags
and setup/1
callbacks. For example, if you are working in a Phoenix app, you can put general
scope enforcement in your test/support/data_case.ex
file:
defmodule MyApp.DataCase do
@moduledoc false
use ExUnit.CaseTemplate
using do
quote do
# Tells [`ExZample`](ExZample.html) which scope you want to look up for your aliases
@moduletag ex_zample_scope: :app_a
import Ecto
import Ecto.Changeset
import Ecto.Query
# import ExZample (optional, import the utility functions like `build/2`, `sequence/1`)
end
end
# Makes [`ExZample`](ExZample.html) narrow the scope of aliases based on the configured tag
# If you have imported the [`ExZample`](ExZample.html), you can do: `setup :ex_zample`
setup &ExZample.ex_zample/1
setup tags do
:ok = Sandbox.checkout(Repo)
unless tags[:async] do
Sandbox.mode(Repo, {:shared, self()})
end
:ok
end
end
Using the the configuration above and narrowing the scope you can have stronger boundary between your Umbrella apps.
Using structs as factories.
All your module need to do to use the ExZample
functions is your implement
the example/0
or example/1
callback.
defmodule MyApp.User do
@behaviour ExZample
defstruct first_name: nil, age: 21
@impl true
def example do
%__MODULE__{first_name: "Abili De Bob", age: 12}
end
end
# later
ExZample.build(MyApp.User)
# => %MyApp.User{first_name: "Abili De Bob", age: 12}
When you implement the example
callback, any module can be a factory.
Defining manually your factory modules
If you want to separate your test data from your app code, you can define a factory in a different module from your struct:
defmodule MyApp.User do
defstruct first_name: nil, age: 21
end
defmodule MyApp.Factories.UserFactory do
@behaviour ExZample
alias MyApp.User
@impl true
def example do
%User{first_name: "Abili De Bob", age: 12}
end
end
# later
alias MyApp.Factories.UserFactory
ExZample.build(UserFactory)
# => %MyApp.User{first_name: "Abili De Bob", age: 12}
You don't to type all this boilerplate code if you use the ExZample.DSL
. You
can implement the example/1
callback when you want to have full control
in how your factories are built:
@impl true
def example(attrs) do
age = Map.get(attrs, :age, 12) * 2
first_name = Map.get(attrs, :first_name, "Abilid") <> " De Bob"
%User{first_name: first_name, age: age}
end
# later
build(:user, first_name: "Alice")
# => %User{first_name: "Alice De Bob", age: 24}
The Example.DSL
also supports the full control of your factories:
factory :user do
import Map, only: [get: 3]
example(attrs) do
%User{
first_name: attrs |> get(:first_name, " De Bob") |> prefix(),
age: get(attrs, :age, 12) * 2,
}
end
defp prefix(string), do: "Abilid #{string}"
end
As you can see, the body of the factory
directive works as any Elixir module.
You can import and define helpers functions.
Manually defining your aliases
If don't want to use the ExZample.DSL
, you can manually define a nickname for your factories. For example, in your test_helper.ex
, after starting ex_zample
, you
can call ExZample.config_aliases/1
.
# in your test_helper.exs
# Don't forget to start :ex_zample app!
:ok = Application.ensure_started(:ex_zample)
# defining manually your aliases
ExZample.config_aliases(%{user: UserFactory})
# later in your app_test.exs
test "activates an user" do
user = ExZample.build(:user)
assert :ok == MyApp.active_user(user)
end
Inspiration
This library was strongly inspired by:
Why not other factories libraries?
Right now you shouldn't change for this one. The other factories libraries has much more features.
However, when your codebase starts to get bigger, it's nice to have a way to split up your factories files in multiple files. Also, it's important when a error happens, it should be explicit and easy to reason about.
Most of other Elixir libraries relies on DLS with macro code, and you need to write macros to split up your factories files. When you get some error in your factory, it's very hard to locate where is the real problem.
This library approach is to rely on vanilla Elixir modules and contracts based on Elixir behaviours. No need to use any macro. The purpose for any macro that can shows up here will be for syntax sugar, not part of the main functionality.
Do I really need a factory library?
Probably not, you can define your own modules to return example structs and insert them with your repo module. However, a factory library can give you some convenient functions for you don't need to reinvent the wheel.