Mock
A mocking libary for the Elixir language.
We use the Erlang meck library to provide module mocking functionality for Elixir. It uses macros in Elixir to expose the functionality in a convenient manner for integrating in Elixir tests.
See the full reference documentation.
Example
For a simple example, if you wanted to test some code which calls
HTTPotion.get to get a webpage but without actually fetching the
webpage you could do something like this.
defmodule MyTest do
use ExUnit.Case, async: false
import Mock
test_with_mock "test_name", HTTPotion,
[get: fn(_url) -> "<html></html>" end] do
HTTPotion.get("http://example.com")
assert called HTTPotion.get("http://example.com")
end
endThe with_mock creates a mock module. The keyword list provides a set
of mock implementation for functions we want to provide in the mock (in
this case just get). Inside with_mock we exercise the test code
and we can check that the call was made as we expected using called and
providing the example of the call we expected (the second argument :_ has a
special meaning of matching anything).
You can also pass the option :passthrough to retain the origina module functionality. For example
defmodule MyTest do
use ExUnit.Case, async: false
import Mock
test_with_mock "test_name", IO, [:passthrough], [] do
IO.puts "hello"
assert called IO.puts "hello"
end
endCurrently, mocking modules cannot be done asynchronously, so make sure that you
are not using async: true in any module where you are testing.
Tips
The use of mocking can be somewhat controversial. I personally think that it works well for certain types of tests. Certainly, you should not overuse it. It is best to write as much as possible of your code as pure functions which don't require mocking to test. However, when interacting with the real world (or web services, users etc.) sometimes side-effects are necessary. In these cases, mocking is one useful approach for testing this functionality.
Also, note that Mock has a global effect so if you are using Mocks in multiple tests set
async: false so that only one test runs at a time.
Help
Open an issue.
Suggestions
I'd welcome suggestions for improvements or bugfixes. Just open an issue.