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ErlyMock is the latest incarnation of an Erlang mocking library inspired by Easymock for Java. It is used in unit tests to verify that a set of functions is called by the code under test in correct order and with correct parameters.
With ErlyMock it is possible to declare the behavior of arbitrary modules/functions with or without expecting acutal invocations. The user simply declares what each function call to some function should return or do at the beginning of a unit test.
The current homepage can be found here: http://erlymock-site.sourceforge.net
- API documentation: http://erlymock-site.sourceforge.net/edoc/index.html
- battle proven in at least three large projects at http://www.lindenbaum.eu
- comprehensive runtime messages
- two-letter module name(we went from 'mock' to 'em', which was quite an improvement for us)
- small, flexible and easy to use API
- allows strict expectations
- allows stub behavior definitions to be intuitively mixed with strict expectations
- correctly restores cover compiled module
- automatic cleanup when mock or test process dies
- implemented with OTP standard behaviour
- because it is a maven project can be automatically installed as maven test dependency
Usually unit test functions using mocks follow a specific pattern:
Assume there are two modules, used by the code to be tested, that shall be mocked (at least to prevent damaging side effects):
A rocket launcher server:
-module(rocket_launcher).
launch(Longitude, Latitude, Type) ->
....And A UI module:
-module(rocket_launcher_ui).
ask_for_instructions() ->
...Then this is how a happy case unit test might look like:
launche_missle_test() ->
% create a new mock process
M = em:new(),
% define the expectations
em:strict(M, rocket_launcher_ui, ask_for_instructions, [],
{return, [{longitude, 123},
{latitude, 999},
{type, some_rocket_type}]}),
em:strict(M, missle_lauchner, launch, [123, 999, some_rocket_type]),
% tell the mock that all expectations are defined
em:replay(M),
% run code under test
rocket_app:interactive(),
% verify expectations
em:verify(M).ErlyMock has undergone many stages and years of development and usage before reaching this stage. It was first published here: http://sheyll.blogspot.com/2009/02/erlang-mock-erlymock.html Then Samual Rivas cleaned it up and added support for restoring cover compiled modules for his project, see http://www.lambdastream.com/. The code was then added with all modifications to the great new erlang-maven-plugin forge which can be found here: http://sourceforge.net/projects/erlang-plugin/.
Then I decided to partially rewrite ErlyMock in order to provide a simpler API and in order to improve the code quality. Also, I wanted to use the gen_fsm OTP standard behavior.