Walkman was inspired by Ruby's VCR. While VCR deals explicitely with HTTP requests, Walkman is useful for performing automated mocking of any module.

Walkman wraps modules instead of modifying them directly, which means there is less funny business going on, so less chance newer versions of Elixir will break the package. Walkman is more explicit and less magical, and as a result you will have to write a tiny bit more boilerplate than you're maybe used to.

Somewhere in your application you've got a module, MyModule, that communicates with the outside world. Perhaps it is an SSH driver, or it makes an HTTP request.

Make the location of this module configurable

# config/config.exs

config :my_app, my_module: MyModule

# config/test.exs

config :my_app, my_module: MyModuleWrapper

Replace MyModule in your application with Application.get_env(:my_app, :my_module).

Wrap MyModule with MyModuleWrapper.

# test/support/my_module_wrapper.ex

require Walkman

Walkman.def_stub(MyModuleWrapper, for: MyModule)

Lastly, in mix.exs, add test/support/ to the paths that need to be compiled in :test.

def project do
  [
    # Everything that usually goes here
    elixirc_paths: elixirc_paths(Mix.env())
  ]
end

defp elixirc_paths(:test), do: ["lib", "test/support"]
defp elixirc_paths(_), do: ["lib"]

Now you can use "tapes" in your tests.

test "MyModule" do
  Walkman.use_tape "my wrapper tape" do
    # test code that uses `MyModule` underwater
  end
end

Add the fixtures that Walkman creates to your repository.

To generate new fixtures, just remove the "tapes" you want to regenerate and re-run the tests. Like VCR, if Walkman doesn't find an existing fixture, it will create one.

Fixtures are saved in Erlang's binary External Term Format, which most editors won't be able to open correctly. If you want to see what exactly has been recorded, you can use :erlang.binary_to_term() to parse the file contents back into readable Elixir terms.

File.read!("path/to/fixture") |> :erlang.binary_to_term()

By default, all Walkman tapes are only available in the scope of the current process. To make the tape available to other processes you have to set global: true:

test "MyModule" do
  Walkman.use_tape "my wrapper tape", global: true do
    # test code that uses `MyModule` underwater
  end
end

The default behaviour can be changed in config/test.exs:

config :walkman, global: true

By default Walkman re-record tapes every time the wrapped module changes and this is done by storing the md5 of the module on the tape.

To change this behaviour the option module_changes should be set to :ignore or :warn which can be done per tape as in the example below:

test "MyModule" do
  Walkman.use_tape "my wrapper tape", module_changes: :warn do
    # test code that uses `MyModule` underwater
  end
end

The module_changes option accepts the following values:

• :rerecord - if the recorded module changes the tape is automatically re-recorded.
• :warn - if the recorded module changes a warning is logged.
• :ignore - It ignores any changes in the recorded module

The default behaviour can also be changed in config/test.exs:

config :walkman, module_changes: :ignore

If you set Walkman to :integration mode then it will pass all function calls through to the wrapped module (instead of using the fixtures).

Walkman.set_mode(:integration)

o Walkman cannot run specs in parallel. Walkman sets the "tape" globally and would have no way of knowing from which test a particular call originates.

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

def deps do
  [
    {:walkman, "~> 0.3.0", only: :test}
  ]
end

Note that if you want to run Walkman's tests locally, you'll need to be running Elixir v1.9.1 and Erlang v22.1.