Elixir - How can you use an alias in doctest?

Question

Is there a way to use a module alias in the doctests? I don't want to have to type out a long name every single time.

defmodule SomeLongModuleName.SubModule do
  alias SomeLongModuleName.SubModule, as: SubModule

  @doc """
      iex> SubModule.method(%{property_a: 1, property_b: 2) # CompileError
      3
  """
  def method(%{property_a: a, property_b: b) do
    a + b
  end
end

The example above shows a situation where I might want to use the alias to avoid long lines. Is it at all possible to use an alias in a doctest?

Answer 1

There are two ways I can think of to not have to type the module name again and again.

1. Use interpolation in your docs and use the aliased name:

   defmodule SomeLongModuleName.SubModule do
     alias SomeLongModuleName.SubModule, as: SubModule
   
     @doc """
         iex> #{SubModule}.method(%{property_a: 1, property_b: 2})
         3
     """
     def method(%{property_a: a, property_b: b}) do
       a + b
     end
   end
   

2. Use just the function name without module and in your call to doctest from your tests, add import: true:

   defmodule SomeLongModuleName.SubModule do
     @doc """
         iex> method(%{property_a: 1, property_b: 2})
         3
     """
     def method(%{property_a: a, property_b: b}) do
       a + b
     end
   end
   

   doctest SomeLongModuleName.SubModule, import: true
   

Answer 2

Building on the answer from lab419 and dylanthepiguy:

Module with doctest:

defmodule SomeLongModuleName.SubModule do
  @doc """
      iex> SubModule.add(x, y)
      3
  """
  def add(x, y) do
    x + y
  end
end

Test case for module with doctest:

defmodule SomeLongModuleName.SubModuleTest do
  use ExUnit.Case, async: true

  # Alias the submodule so we don't have to use the fully qualified name 
  alias SomeLongModuleName.SubModule

  doctest SomeLongModuleName.SubModule, import: true
end

Answer 3

As mentioned by dylanthepiguy it is definitely a better solution to put the aliases into the testfile, just before the doctest line.

Instrumenting your code for tests is IMHO a code smell.

Also note that as: Submodule is the default and therefore unnecessary.

Answer 4

It turns out you can put a alias SomeLongModuleName.SubModule, as: SubModule line just before the test.

A better solution is to not put too many tests in the docs, and not use an alias. Then, in your test file you can put alias SomeLongModuleName.SubModule, as: SubModule to save.