ExMachina makes it easy to create test data and associations. It works great with Ecto, but is configurable to work with any persistence library.
This README follows the main branch, which may not be the currently published version. Here are the docs for the latest published version of ExMachina.
In mix.exs, add the ExMachina dependency:
def deps do
[
{:ex_machina, "~> 2.8.0", only: :test},
]
endAdd your factory module inside test/support so that it is only compiled in the
test environment.
Next, be sure to start the application in your test/test_helper.exs before
ExUnit.start:
{:ok, _} = Application.ensure_all_started(:ex_machina)You will follow the same instructions as above, but you will also need to add
test/support to your compilation paths (elixirc_paths) if you have not done
so already.
In mix.exs, add test/support to your elixirc_paths for just the test env.
def project do
[app: ...,
# Add this if it's not already in your project definition.
elixirc_paths: elixirc_paths(Mix.env)]
end
# This makes sure your factory and any other modules in test/support are compiled
# when in the test environment.
defp elixirc_paths(:test), do: ["lib", "test/support"]
defp elixirc_paths(_), do: ["lib"]Check out the docs for more details.
Define factories:
defmodule MyApp.Factory do
# with Ecto
use ExMachina.Ecto, repo: MyApp.Repo
# without Ecto
use ExMachina
def user_factory do
%MyApp.User{
name: "Jane Smith",
email: sequence(:email, &"email-#{&1}@example.com"),
role: sequence(:role, ["admin", "user", "other"]),
}
end
def article_factory do
title = sequence(:title, &"Use ExMachina! (Part #{&1})")
# derived attribute
slug = MyApp.Article.title_to_slug(title)
%MyApp.Article{
title: title,
slug: slug,
# another way to build derived attributes
tags: fn article ->
if String.contains?(article.title, "Silly") do
["silly"]
else
[]
end
end,
# associations are inserted when you call `insert`
author: build(:user)
}
end
# derived factory
def featured_article_factory do
struct!(
article_factory(),
%{
featured: true,
}
)
end
def comment_factory do
%MyApp.Comment{
text: "It's great!",
article: build(:article),
}
end
endUsing factories (check out the docs for more details):
# `attrs` are automatically merged in for all build/insert functions.
# `build*` returns an unsaved comment.
# Associated records defined on the factory are built.
attrs = %{body: "A comment!"} # attrs is optional. Also accepts a keyword list.
build(:comment, attrs)
build_pair(:comment, attrs)
build_list(3, :comment, attrs)
# `insert*` returns an inserted comment. Only works with ExMachina.Ecto
# Associated records defined on the factory are inserted as well.
insert(:comment, attrs)
insert_pair(:comment, attrs)
insert_list(3, :comment, attrs)
# `params_for` returns a plain map without any Ecto specific attributes.
# This is only available when using `ExMachina.Ecto`.
params_for(:comment, attrs)
# `params_with_assocs` is the same as `params_for` but inserts all belongs_to
# associations and sets the foreign keys.
# This is only available when using `ExMachina.Ecto`.
params_with_assocs(:comment, attrs)
# Use `string_params_for` to generate maps with string keys. This can be useful
# for Phoenix controller tests.
string_params_for(:comment, attrs)
string_params_with_assocs(:comment, attrs)build/2 is a function call. As such, it gets evaluated immediately. So this
code:
insert_pair(:account, user: build(:user))Is equivalent to this:
user = build(:user)
insert_pair(:account, user: user) # same user for both accountsSometimes that presents a problem. Consider the following factory:
def user_factory do
%{name: "Gandalf", email: sequence(:email, "gandalf#{&1}@istari.com")}
endIf you want to build a separate user per account, then calling
insert_pair(:account, user: build(:user)) will not give you the desired
result.
In those cases, you can delay the execution of the factory by passing it as an anonymous function:
insert_pair(:account, user: fn -> build(:user) end)You can also do that in a factory definition:
def account_factory do
%{user: fn -> build(:user) end}
endYou can even accept the parent record as an argument to the function:
def account_factory do
%{user: fn account -> build(:user, vip: account.premium) end}
endNote that the account passed to the anonymous function is only the struct
after it's built. It's not an inserted record. Thus, it does not have data that
is only accessible after being inserted into the database (e.g. id).
By default, ExMachina will merge the attributes you pass into build/insert into your factory. But if you want full control of your attributes, you can define your factory as accepting one argument, the attributes being passed into your factory.
def custom_article_factory(attrs) do
title = Map.get(attrs, :title, "default title")
article = %Article{
author: "John Doe",
title: title
}
# merge attributes and evaluate lazy attributes at the end to emulate
# ExMachina's default behavior
article
|> merge_attributes(attrs)
|> evaluate_lazy_attributes()
endNOTE that in this case ExMachina will not merge the attributes into your factory, and it will not evaluate lazy attributes. You will have to do this on your own if desired.
Because you have full control of the factory when defining it with one argument, you can build factories that are neither maps nor structs.
# factory definition
def room_number_factory(attrs) do
%{floor: floor_number} = attrs
sequence(:room_number, &"#{floor_number}0#{&1}")
end
# example usage
build(:room_number, floor: 5)
# => "500"
build(:room_number, floor: 5)
# => "501"NOTE that you cannot use non-map factories with Ecto. So you cannot
insert(:room_number).
# Example of use in Phoenix with a factory that uses ExMachina.Ecto
defmodule MyApp.MyModuleTest do
use MyApp.ConnCase
# If using Phoenix, import this inside the using block in MyApp.ConnCase
import MyApp.Factory
test "shows comments for an article" do
conn = conn()
article = insert(:article)
comment = insert(:comment, article: article)
conn = get conn, article_path(conn, :show, article.id)
assert html_response(conn, 200) =~ article.title
assert html_response(conn, 200) =~ comment.body
end
endIf you are using ExMachina in all environments:
Start by creating one factory module (such as
MyApp.Factory) inlib/my_app/factory.exand putting all factory definitions in that module.
If you are using ExMachina in only the test environment:
Start by creating one factory module (such as
MyApp.Factory) intest/support/factory.exand putting all factory definitions in that module.
Later on you can easily create different factories by creating a new module in the same directory. This can be helpful if you need to create factories that are used for different repos, your factory module is getting too big, or if you have different ways of saving the record for different types of factories.
This example shows how to set up factories for the testing environment. For setting them in all environments, please see the To install in all environments section
Start by creating main factory module in
test/support/factory.exand name itMyApp.Factory. The purpose of the main factory is to allow you to include only a single module in all tests.
# test/support/factory.ex
defmodule MyApp.Factory do
use ExMachina.Ecto, repo: MyApp.Repo
use MyApp.ArticleFactory
endThe main factory includes MyApp.ArticleFactory, so let's create it next. It might be useful to create a separate directory for factories, like test/factories. Here is how to create a factory:
# test/factories/article_factory.ex
defmodule MyApp.ArticleFactory do
defmacro __using__(_opts) do
quote do
def article_factory do
%MyApp.Article{
title: "My awesome article!",
body: "Still working on it!"
}
end
end
end
endThis way you can split your giant factory file into many small files. But what about name conflicts? Use pattern matching to avoid them!
# test/factories/post_factory.ex
defmodule MyApp.PostFactory do
defmacro __using__(_opts) do
quote do
def post_factory do
%MyApp.Post{
body: "Example body"
}
end
def with_comments(%MyApp.Post{} = post) do
insert_pair(:comment, post: post)
post
end
end
end
end
# test/factories/video_factory.ex
defmodule MyApp.VideoFactory do
defmacro __using__(_opts) do
quote do
def video_factory do
%MyApp.Video{
url: "example_url"
}
end
def with_comments(%MyApp.Video{} = video) do
insert_pair(:comment, video: video)
video
end
end
end
endIf you place your factories outside of test/support make sure they will compile by adding that directory to the compilation paths in your mix.exs file. For example for the test/factories files above you would modify your file like so:
# ./mix.exs
...
defp elixirc_paths(:test), do: ["lib", "test/factories", "test/support"]
...ExMachina will automatically save any associations when you call any of the
insert functions. This includes belongs_to and anything that is
inserted by Ecto when using Repo.insert!, such as has_many, has_one,
and embeds. Since we automatically save these records for you, we advise that
factory definitions only use build/2 when declaring associations, like so:
def article_factory do
%Article{
title: "Use ExMachina!",
# associations are inserted when you call `insert`
comments: [build(:comment)],
author: build(:user),
}
endUsing insert/2 in factory definitions may lead to performance issues and bugs,
as records will be saved unnecessarily.
ExMachina.Ecto uses
Repo.insert!/2 to
insert records into the database. Sometimes you may want to pass options to deal
with multi-tenancy or return some values generated by the database. In those
cases, you can use c:ExMachina.Ecto.insert/3:
For example,
# return values from the database
insert(:user, [name: "Jane"], returning: true)
# use a different prefix
insert(:user, [name: "Jane"], prefix: "other_tenant")def make_admin(user) do
%{user | admin: true}
end
def with_article(user) do
insert(:article, user: user)
user
end
build(:user) |> make_admin |> insert |> with_articleIf you want to keep the factories somewhere other than test/support,
change this line in mix.exs:
# Add the folder to the end of the list. In this case we're adding `test/factories`.
defp elixirc_paths(:test), do: ["lib", "test/support", "test/factories"]You can use ExMachina without Ecto, by using just the build functions, or you
can define one or more custom strategies to use in your factory. You can also
use custom strategies with Ecto. Here's an example of a strategy for json
encoding your factories. See the docs on ExMachina.Strategy for more info.
defmodule MyApp.JsonEncodeStrategy do
use ExMachina.Strategy, function_name: :json_encode
def handle_json_encode(record, _opts) do
Poison.encode!(record)
end
end
defmodule MyApp.Factory do
use ExMachina
# Using this will add json_encode/2, json_encode_pair/2 and json_encode_list/3
use MyApp.JsonEncodeStrategy
def user_factory do
%User{name: "John"}
end
end
# Will build and then return a JSON encoded version of the user.
MyApp.Factory.json_encode(:user)Before opening a pull request, please open an issue first.
git clone https://github.com/thoughtbot/ex_machina.git
cd ex_machina
mix deps.get
mix test
Once you've made your additions and mix test passes, go ahead and open a PR!
ExMachina is Copyright © 2015 thoughtbot. It is free software, and may be redistributed under the terms specified in the LICENSE file.
ExMachina is maintained and funded by thoughtbot, inc. The names and logos for thoughtbot are trademarks of thoughtbot, inc.
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