stephanos
Hi everyone,
I wanted to share rewire with you, a dependency injection library I’ve been working on over the last few weeks. It aims to keep your production code free from testing concerns, works with async tests and any mock.
Example
Given a module such as this:
# this module has a hard-wired dependency on the `English` module
defmodule Conversation do
def start(), do: English.greet()
end
If you define a mox mock EnglishMock you can rewire the dependency in your unit test:
defmodule MyTest do
use ExUnit.Case
use Rewire # (1) activate `rewire`
import Mox
rewire Conversation, English: EnglishMock # (2) rewire `English` to `EnglishMock`
test "start/0" do
stub(EnglishMock, :greet, fn -> "g'day" end)
assert Conversation.start() == "g'day" # (3) test using the mock
end
end
Check out all the details at:
https://github.com/stephanos/rewire
And let me know what you think!
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hauleth
Looks nice except one thing - why use
useinstead just plainimport? It should work without problems.marcin
That’s cool! I’ve been struggling in how to organise a callback mechanism (eg. after creating the record send an email and also generate a receipt), but keep it decoupled enough to be able to test well.
Rewire could help here! Will check it out.
edisonywh
Very interesting. Since it works by aliasing, does that mean it can only be used for unit testing the module directly? For example, if I have a module called
Discord, andDiscordcallsConversation.start/0, there’s no way to rewire theEnglishreference, is that right?hauleth
From what I see in the code - yes, it works only for modules called directly.
stephanos
you’re absolutely right! I originally had some compiler hooks in there to update the module attributes but never went back to
requireafter I realized I didn’t need that.Just updated the docs and shipped a new version to reflect that.
stephanos
actually, you could stack them:
You can find a working test case here: rewire/test/rewire_alias_test.exs at master · stephanos/rewire · GitHub
But I’m not sure whether that’s a good testing etiquette. Reaching deeply into module’s might be a smell, depending on the use case.
ruhshan
Hi, very cool!
Is there any way to use it with like… where I declare dependency using compile_env
For example:
hauleth
It should work just fine if you will mock module that is defined as comp-time config.