Stub Alias

A simple macro to allow switching alias statements out with different values based upon environment.

Installation

If available in Hex, the package can be installed as:

Add stub_alias to your list of dependencies in mix.exs:

def deps do
  [{:stub_alias, "~> 0.1.0"}]
end

StubAlias is a compile time dependency and can be left out of the applications list.

Usage

In your code you may have some alias statements like the following:

EXAMPLE

defmodule MyModule do
  alias MyModule.Foo

  def stuff() do
    Foo.do_something_with_side_effects
  end
end

Obviously, during testing, it makes it more difficult to test the function stuff/0 since it calls another function which has undesierable side effects (or requires some system state like a running GenServer).

If you add to your config/test.exs configuration like the following:

config :stub_alias,
  "MyModule.Foo": MyModule.Stubs.Foo

Setup your mix.exs to compile in the test/support folder like in Phoenix. Then replace alias MyModule.Foo with stub_alias MyModule.Foo (after import StubAlias of course):

SOLUTION

lib/my_module.ex

defmodule MyModule do
  import StubAlias
  stub_alias MyModule.Foo

  def stuff() do
    Foo.do_something_with_side_effects
  end
end

test/support/foo.ex

defmodule MyModule.Stubs.Foo do
  def do_something_with_side_effects() do
    # Return hard coded data or get data from an agent or whatever you please
    results = %{}
    results
  end
end

In the :test Mix.env, your aliases will be replaced as desired. This then allows you to have a compiled test/support folder which supplies those stubs, making easy explicit replacements of code at test time.