View Source 🥣 Blend

Test your package against different versions of its dependencies.

Generates and maintains multiple lockfiles based on your defined variations (a.k.a. blends) so that you can test your package against different variations of your dependencies versions.

You can read more about the motivation for this project here.

Installation

If available in Hex, the package can be installed by adding blend to your list of dependencies in mix.exs:

def deps do
  [
    {:blend, "~> 0.4.1", only: :dev}
  ]
end

Usage

1. Generate `blend.exs`

mix blend.install

2. Define your blends

Edit and set your blends in the blend.exs file.

For example, an elixir package that depends on plug_crypto with a requirement of ~> 1.2 or ~> 2.0, that wants to test against the two major versions, would normally have it's mix.lock resolved to 2.x, so it would want to define the following:

# blend.exs

# Example for testing against plug_crypto 1.x
%{
  plug_crypto_1: [{:plug_crypto, "~> 1.2"}]
}

in order for blend to generate an additional lockfile that locks plug_crypto to the latest possible 1.x supported version.

Map keys define the blend name, used for naming the lockfile, and the dependencies list are merged with the package dependencies before resolving and generating the lockfile variation.

3. Resolve blends and generate lockfiles

mix blend.get

to resolve your blends and generate new lockfiles with variations of your dependencies under the new /blend folder.

blend
├── _build
├── deps
├── plug_crypto_1.mix.lock
mix.lock

4. Ignore blend build artifacts

 # .gitignore

 ...

+/blend/_build
+/blend/deps

Add to your .gitignore file, before comitting your changes.

5. Running tasks in the context of a blend lockfile

Option A. Overriding your `mix.lock`.

If you just need to quickly run against a blend lockfile (e.g. in a CI job step), it might be enough to just:

cp blend/plug_crypto_1.mix.lock mix.lock

before your mix deps.get step.

After that you can run any additional task, e.g. run your tests or your phx.server, which will run in the context of the specific blend lockfile copied.

mix test

mix phx.server

Option B. `BLEND` env var configuration

A more permanent configuration for running mix tasks in the context of a blend lockfile with a simple env var can be accomplished by customizing your mix.exs a bit, with the following steps.

1. Create a new file `blend/premix.exs` with the following command:

mix blend.gen.premix

This will generate a blend/premix.exs file that needs to be compiled at the top of your mix.exs file so that some mix env vars are properly set based on the BLEND env var before running any mix task.

2. Modify your `mix.exs`.

 # mix.exs

+if File.exists?("blend/premix.exs") do
+  Code.compile_file("blend/premix.exs")
+end

 defmodule YourApp.MixProject do
   ...
   def project do
     [
       ...
     ]
+    |> Keyword.merge(maybe_lockfile_option())
   end
   ....

+  defp maybe_lockfile_option do
+    case System.get_env("MIX_LOCKFILE") do
+      nil -> []
+      "" -> []
+      lockfile -> [lockfile: lockfile]
+     end
+  end
 end

3. Enjoy

Now you can run any task, e.g. run your tests or your server, against different lockfiles locally by just prepending the proper environment variable value:

BLEND=plug_crypto_1 mix test

BLEND=plug_crypto_1 mix phx.server

Tasks

mix blend.install      # Generate blend.exs
mix blend.get          # Generate blend lockfiles
mix blend.update --all # Update blend lockfiles to latest possible versions
mix blend.list         # List blends
mix blend.clean        # Cleans blends build artifacts and stale lockfiles
mix blend.gen.premix   # Generate premix.exs file

Motivation

At Mimiquate, our engagement with the Elixir ecosystem deeply influences our projects. We’ve benefited immensely from the community’s support and resources. During our development of open-source hex packages, we encountered a challenge: testing across different dependency versions lacked a straightforward approach. This issue led us to think about how we could contribute to the community that has been so supportive of us.

Our background includes Ruby on Rails, where the Ruby community has tackled a similar challenge with the appraisal gem. This tool makes it easier to test various dependency versions and is designed to work well with CI pipelines, reducing the risk of regressions. It’s been really great for developers and has positively impacted the ecosystem’s health.

With that inspiration, we set out to create something for the Elixir community to help streamline development. Our first version doesn’t have all the functionalities of the appraisal gem but establishes a good starting point. It allows developers to test their hex packages against different lock file combinations, which is handy for spotting regressions in common scenarios.

We realize that our current tool doesn’t address every testing scenario. Yet, we’re committed to improving it, aiming to cover more ground and enhance its functionality. Our goal goes beyond just solving a technical issue; we hope to make the development process in the Elixir community more supportive and efficient for everyone.

Having a hard time finding Elixir talent?

At Mimiquate we have been Elixiring since 2016 and we are true believers in the community and the ecosystem. If you are looking to turbo charge your Elixir team, reach out!

License

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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