A mocking library for Erlang.
See what's new in 0.8 Release Notes.
- Dynamic return values using sequences and loops of static values
- Compact definition of mock arguments, clauses and return values
- Pass through: call functions in the original module
- Complete call history showing calls, return values and exceptions
- Mock validation, will invalidate mocks that were not called correctly
- Throwing of expected exceptions that keeps the module valid
- Throws an error when mocking a module that doesn't exist or has been
renamed (disable with option
non_strict) - Support for Hamcrest matchers
- Automatic backup and restore of cover data
- Mock is linked to the creating process and will unload automatically
when a crash occurs (disable with option
no_link) - Mocking of sticky modules (using the option
unstick)
Here's an example of using Meck in the Erlang shell:
Eshell V5.8.4 (abort with ^G)
1> meck:new(dog, [non_strict]). % non_strict is used to create modules that don't exist
ok
2> meck:expect(dog, bark, fun() -> "Woof!" end).
ok
3> dog:bark().
"Woof!"
4> meck:validate(dog).
true
5> meck:unload(dog).
ok
6> dog:bark().
** exception error: undefined function dog:bark/0Exceptions can be anticipated by Meck (resulting in validation still passing). This is intended to be used to test code that can and should handle certain exceptions indeed does take care of them:
5> meck:expect(dog, meow, fun() -> meck:exception(error, not_a_cat) end).
ok
6> catch dog:meow().
{'EXIT',{not_a_cat,[{meck,exception,2},
{meck,exec,4},
{dog,meow,[]},
{erl_eval,do_apply,5},
{erl_eval,expr,5},
{shell,exprs,6},
{shell,eval_exprs,6},
{shell,eval_loop,3}]}}
7> meck:validate(dog).
trueNormal Erlang exceptions result in a failed validation. The following example is just to demonstrate the behavior, in real test code the exception would normally come from the code under test (which should, if not expected, invalidate the mocked module):
8> meck:expect(dog, jump, fun(Height) when Height > 3 ->
erlang:error(too_high);
(Height) ->
ok
end).
ok
9> dog:jump(2).
ok
10> catch dog:jump(5).
{'EXIT',{too_high,[{meck,exec,4},
{dog,jump,[5]},
{erl_eval,do_apply,5},
{erl_eval,expr,5},
{shell,exprs,6},
{shell,eval_exprs,6},
{shell,eval_loop,3}]}}
11> meck:validate(dog).
falseHere's an example of using Meck inside an EUnit test case:
my_test() ->
meck:new(my_library_module),
meck:expect(my_library_module, fib, fun(8) -> 21 end),
?assertEqual(21, code_under_test:run(fib, 8)), % Uses my_library_module
?assert(meck:validate(my_library_module)),
meck:unload(my_library_module).Pass-through is used when the original functionality of a module
should be kept. When the option passthrough is used when calling
new/2 all functions in the original module will be kept in the
mock. These can later be overridden by calling expect/3 or
expect/4.
Eshell V5.8.4 (abort with ^G)
1> meck:new(string, [unstick, passthrough]).
ok
2> string:strip(" test ").
"test"It's also possible to pass calls to the original function allowing us
to override only a certain behavior of a function (this usage is
compatible with the passthrough option). passthrough/1 will always
call the original function with the same name as the expect is
defined in):
Eshell V5.8.4 (abort with ^G)
1> meck:new(string, [unstick]).
ok
2> meck:expect(string, strip, fun(String) -> meck:passthrough([String]) end).
ok
3> string:strip(" test ").
"test"
4> meck:unload(string).
ok
5> string:strip(" test ").
"test"Meck requires make and rebar to build. To build Meck go to the Meck directory
and simply type:
makeIn order to run all tests for Meck type the following command from the same directory:
make testTwo things might seem alarming when running the tests:
- Warnings emitted by cover
- En exception printed by SASL
Both are expected due to the way Erlang currently prints errors. The
important line you should look for is All XX tests passed, if that
appears all is correct.
Documentation can be generated through the use of the following command:
make docMeck is best used via rebar. Add the following dependency t
your rebar.config in your project root:
{deps, [
{meck, ".*",
{git, "https://github.com/eproxus/meck.git", {tag, "0.8.2"}}}
]}.If you want to install your own built version of Meck add the ebin
directory to your Erlang code path or move the Meck folder into your
release folder and make sure that folder is in your ERL_LIBS
environment variable.
Meck will have trouble mocking certain modules since Meck works by recompiling and reloading modules. Since Erlang have a flat module namespace, replacing a module has to be done globally in the Erlang VM. This means certain modules cannot be mocked. The following is a non-exhaustive list of modules that can either be problematic to mock or not possible at all:
erlangoscryptocompile
Patches are greatly appreciated! For a much nicer history, please
[write good commit messages][5]. Use a branch name prefixed by
feature/ (e.g. feature/my_example_branch) for easier integration
when developing new features or fixes for meck.
Should you find yourself using Meck and have issues, comments or feedback please create an issue here on GitHub.
Contributors:
- Maxim Vladimirsky (@horkhe)
- Ryan Zezeski (@rzezeski)
- David Haglund (@daha)
- Magnus Henoch (@legoscia)
- Susan Potter (@mbbx6spp)
- Andreas Amsenius (@adbl)
- Anthony Molinaro (@djnym)
- Matt Campbell (@xenolinguist)
- Martynas Pumputis (@brb)
- Shunichi Shinohara (@shino)
- Miëtek Bak
- Henry Nystrom
- Ward Bekker (@wardbekker)
- Damon Richardson
- Christopher Meiklejohn
- Joseph Wayne Norton (@norton)
- Erkan Yilmaz (@Erkan-Yilmaz)
- Joe Williams (@joewilliams)
- Russell Brown
- Michael Klishin (@michaelklishin)
- Magnus Klaar