# Stub Alias []()
A simple macro to allow switching `alias` statements out with different values based upon environment.
## Installation
[Available in Hex](https://hex.pm/packages/stub_alias), 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**
```elixir
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:
```elixir
config :stub_alias,
"MyModule.Foo": MyModule.Stubs.Foo
```
Setup your mix.exs to compile in the `test/support` folder [like in Phoenix](https://github.com/phoenixframework/phoenix/blob/master/installer/templates/new/mix.exs#L12). Then replace `alias MyModule.Foo` with `stub_alias MyModule.Foo` (after `import StubAlias` of course):
**SOLUTION**
`lib/my_module.ex`
```elixir
defmodule MyModule do
import StubAlias
stub_alias MyModule.Foo
def stuff() do
Foo.do_something_with_side_effects
end
end
```
`test/support/foo.ex`
```elixir
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.
