Definject - Unobtrusive Dependency Injector for Elixir

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1

Hello,

I just published version 1.1 of definject. It aims to make dependency injection unobtrusive.

import Definject

definject send_welcome_email(user_id) do
  %{email: email} = Repo.get(User, user_id)

  welcome_email(to: email)
  |> Mailer.send()
end

is expanded into (simplified for understanding)

def send_welcome_email(user_id, deps \\ %{}) do
  %{email: email} = Map.get(deps, &Repo.get/2, &Repo.get/2).(User, user_id)

  welcome_email(to: email)
  |> Map.get(deps, &Mailer.send/1, &Mailer.send/1).()
end

Then, you can inject mock functions and modules in tests.

test "send_welcome_email" do
  Accounts.send_welcome_email(100, %{
    Repo => MockRepo,
    &Mailer.send/1 => fn %Email{to: "user100@gmail.com", subject: "Welcome"} ->
      Process.send(self(), :email_sent)
    end
  })

  assert_receive :email_sent
end

definject does not require you to modify function arguments or body. Instead, you just need to replace def with definject . It also allows injecting different mocks to each function. It also does not limit using :async option as mocks are contained in each test function.

You can find definject here:

Thanks!

6 Likes
2

Hey,

What’s the difference between definject and mox?

3

Awesome, thank you @jechol :clap:

Any ideas how to get VSCode to highlight the definject statements properly? :laughing:

I suggest you link to Hexdocs somewhere at the top of the README.md, would be handy.

4

Typically with Mox you sub out the module name at compile time and at test time you bind in functions. This cleverly uses registry, $callers and $ancestors (I think) to make sure tests get isolated mocks.

With definject, the function is majorly fiddled with (basically rewritten) so that you don’t have to do that compile-time module substitution.

I would be worried that definject is more brittle and has more corner cases, but it’s the sort of thing where if it works for you it’ll work really well.

2 Likes
5

I added documentation section just now, although content is almost same with README.
But, I have no idea how to make it highlighted in VSCode.

If you need it be formatted like def, add
locals_without_parens: [definject: 1, definject: 2]

6

@ityonemo explained well.

You can read more at Why?