Stubr v1.4.0

A large update has been made to Stubr including the introduction of spies and a large collection of functions like called_with?, called_once?, returns?, etc… The full documentation is available in hexdocs.

About Stubr

Stubr is a set of functions helping people to create stubs and spies in Elixir.

In Elixir, you should aim to write pure functions. However, sometimes you need to write functions that post to external API’s or functions that depend on the current time. Since these actions can lead to side effects, they can make it harder to unit test your system.

Stubr solves this problem by taking cues from mocks and explicit contracts. It provides a set of functions that help people create “mocks as nouns” and not “mocks as verbs”:

iex> stub = Stubr.stub!([foo: fn _ -> :ok end], call_info: true)
iex> stub.foo(1)
:ok
iex> stub |> Stubr.called_once?(:foo)
true

iex> spy = Stubr.spy!(Float)
iex> spy.ceil(1.5)
iex> spy |> Stubr.called_with?(:ceil, [1.5])
true
iex> spy |> Stubr.called_twice?(:ceil)
false

Examples

Stubs

Stubs can be created using stub!/1 and stub!/2:

iex> stub = Stubr.stub!([foo: fn -> :bar end])
iex> stub.foo()
:bar

iex> stub = Stubr.stub!([foo: fn _ -> :bar end], call_info: true)
iex> stub.foo(:baz)
iex> stub |> Stubr.called_with?(:foo, [:baz])
true

The input to these functions is a keyword list of function names
(expressed as atoms) and their implementations (expressed as
anonymous functions):

[function_name: (...) -> any()]

Additionally, takes an optional keyword list to configure the stub.

Options

The options available to stub!/2 are:

• :module - when set, if the module does not contain a function
  defined in the keyword list, then raises an UndefinedFunctionError

• :auto_stub - when true and a module has been set, if there
  is not a matching function, then defers to the module function
  (defaults to false)

• behaviour - when set, raises a warning if the stub does not
  implement the behaviour

• call_info - when set, if a function is called, records the input
  and the output to the function. Accessed by calling
  Stubr.call_info(stub, :function_name)
  (defaults to false)

Spies

Spies can be created using spy!/1:

iex> spy = Stubr.spy!(Float)
iex> spy.ceil(1.5)
iex> spy |> Stubr.called_with?(:ceil, [1.5])
true
iex> spy |> Stubr.called_twice?(:ceil)
false

Random numbers

It is easy to use Stubr.stub! to set up a stub for the uniform/1 function in the :rand module. Note, there is no need to explicitly set the module option, it is just used to make sure the uniform/1 function exists in the :rand module.

test "create a stub of the :rand.uniform/1 function" do
  rand_stub = Stubr.stub!([uniform: fn _ -> 1 end], module: :rand)

  assert rand_stub.uniform(1) == 1
  assert rand_stub.uniform(2) == 1
  assert rand_stub.uniform(3) == 1
  assert rand_stub.uniform(4) == 1
  assert rand_stub.uniform(5) == 1
  assert rand_stub.uniform(6) == 1
end

Timex

As above, we can use Stubr.stub! to stub the Timex.now/0 function in the Timex module. However, we also want the stub to defer to the original functionality of the Timex.before?/2 function. To do this, we just set the module option to Timex and the auto_stub option to true.

test "create a stub of Timex.now/0 and defer on all other functions" do
  fixed_time = Timex.to_datetime({2999, 12, 30})

  timex_stub = Stubr.stub!([now: fn -> fixed_time end], module: Timex, auto_stub: true)

  assert timex_stub.now == fixed_time
  assert timex_stub.before?(fixed_time, timex_stub.shift(fixed_time, days: 1))
end

HTTPoison

In this example, we create stubs of the functions get and post in the HTTPoison module that return different values dependant on their inputs:

setup_all do
  http_poison_stub = Stubr.stub!([
    get: fn("www.google.com") -> {:ok, %HTTPoison.Response{body: "search", status_code: 200}} end,
    get: fn("www.nasa.com") -> {:ok, %HTTPoison.Response{status_code: 401}} end,
    post: fn("www.nasa.com", _) -> {:error, %HTTPoison.Error{reason: :econnrefused}} end
  ], module: HTTPoison)

  [stub: http_poison_stub]
end

test "create a stub of HTTPoison.get/1", context do
  {:ok, google_response} = context[:stub].get("www.google.com")
  {:ok, nasa_response} = context[:stub].get("www.nasa.com")

  assert google_response.body == "search"
  assert google_response.status_code == 200
  assert nasa_response.status_code == 401
end

test "create a stub of HTTPoison.post/2", context do
  {:error, error} = context[:stub].post("www.nasa.com", "any content")

  assert error.reason == :econnrefused
end