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W0068 - meck_restricted

Severity: Error

Problem​

This diagnostic reports an error when mocking certain restricted modules using meck:new/2 or meck:expect/3,4 in tests.

Example​

-module(my_SUITE).

init_per_testcase(_TestCase, Config) ->
    meck:new(restricted_mod, [passthrough]),
%%  ^^^^^^^^^^^ 💡 error: W0068: Mocking 'restricted_mod' is almost always the wrong approach

    meck:expect(restricted_mod, some_function, 1, ok),
%%  ^^^^^^^^^^^ 💡 error: W0068: Mocking 'restricted_mod' is almost always the wrong approach
    % ...

Explanation​

Certain core infrastructure modules should not be mocked in tests because mocking them can hide real bugs that would only surface in production. In addition, it makes it harder to make foundational changes to these modules.

How to Fix​

Instead of mocking restricted modules, use the real module APIs or dedicated test utilities:

  1. Use the module's own test helpers or generators to set up the state you need
  2. Consider refactoring the code under test to accept the relevant values as parameters

Adding More Restricted Modules​

To add more modules to this linter, edit the RESTRICTED_MODULES constant in meck_restricted.rs.