A simple Elixir package to elegantly mock module functions within (asynchronous) ExUnit tests using Erlang's :meck
library
To install MecksUnit, please do the following:
-
Add mecks_unit to your list of dependencies in
mix.exs
:def deps do [ {:mecks_unit, "~> 0.1.6", only: :test} ] end
Mocking module functions is pretty straightforward and done as follows:
- Add
use MecksUnit.Case
at the beginning of your test file - Use
defmock
as if you would define the original module withdefmodule
containing mocked functions - Use
mocked_test
as if you would define a normal ExUnittest
after having defined all the required mock modules - Add
MecksUnit.mock()
in yourtest/test_helper.exs
file - Enjoy ;)
Please note that the defined mock modules only apply to the first mocked_test
encountered.
So they are isolated (despite of :meck
having an unfortunate global effect) as MecksUnit takes care of it.
Also, non-matching function heads within the mock module will result in invoking the original module function as well.
As of version 0.1.2
, you can assert function calls using called
(returns a boolean) or assert_called
(raises an
error when not having found a match) within your test block. Use _
to match any argument as if you would pattern match.
Prior to version 0.1.3
, you would very often get :meck
related compile errors when using MecksUnit in multiple test files.
From that version on, this problem is solved. Happy testing! ^^
The following is a working example defined in test/mecks_unit_test.exs
# (in test/test_helper.exs)
ExUnit.start()
MecksUnit.mock()
# (in test/mecks_unit_test.exs)
defmodule Foo do
def trim(string) do
String.trim(string)
end
end
defmodule MecksUnitTest do
use ExUnit.Case, async: true
use MecksUnit.Case
defmock String do
def trim(" Paul "), do: "Engel"
def trim(" Foo ", "!"), do: "Bar"
def trim(_, "!"), do: {:passthrough, [" Surprise! !!!!", "!"]}
def trim(_, _), do: :passthrough
end
defmock List do
def wrap(:foo), do: [1, 2, 3, 4]
end
mocked_test "using mocked module functions" do
task =
Task.async(fn ->
assert "Engel" == String.trim(" Paul ")
assert "Engel" == Foo.trim(" Paul ")
assert "Bar" == String.trim(" Foo ", "!")
assert " Surprise! " == String.trim(" Paul ", "!")
assert "MecksUnit" == String.trim(" MecksUnit ")
assert "Paul Engel" == String.trim(" Paul Engel ", " ")
assert [1, 2, 3, 4] == List.wrap(:foo)
assert [] == List.wrap(nil)
assert [:bar] == List.wrap(:bar)
assert [:foo, :bar] == List.wrap([:foo, :bar])
assert called List.wrap(:foo)
assert_called String.trim(_)
end)
Task.await(task)
end
test "using the original module functions" do
task =
Task.async(fn ->
assert "Paul" == String.trim(" Paul ")
assert "Paul" == Foo.trim(" Paul ")
assert " Foo " == String.trim(" Foo ", "!")
assert " Paul " == String.trim(" Paul ", "!")
assert "MecksUnit" == String.trim(" MecksUnit ")
assert "Paul Engel" == String.trim(" Paul Engel ", " ")
assert [:foo] == List.wrap(:foo)
assert [] == List.wrap(nil)
assert [:bar] == List.wrap(:bar)
assert [:foo, :bar] == List.wrap([:foo, :bar])
end)
Task.await(task)
end
end
Please note that you can delegate to the original implementation by either returning :passthrough
(which forwards the given arguments)
or return a tuple {:passthrough, arguments}
in which you can alter the arguments yourself.
Unlike Mock, MecksUnit supports running mocked tests asynchronously. W00t! ^^
Copyright (c) 2019 Paul Engel, released under the MIT License
http://github.com/archan937 – http://twitter.com/archan937 – pm_engel@icloud.com
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.