How do I mock multiple modules in one Elixir test?

Use the `with_mocks` macro to define a list of modules and their mock functions, as shown in the README example with Map and String modules, allowing concurrent mocking in a single test block.

Mock vs Mox: which is better for Elixir testing?

Mock is simpler for quick module mocking with macros, ideal for basic tests, while Mox is better for defining explicit behaviors and contracts, especially in larger codebases with dependency injection.

Can I mock internal function calls with the Mock library?

No, Mock does not support mocking internal calls; you must refactor code to use fully qualified names like `__MODULE__.function()` or `Module.function()`, as explained in the 'NOT SUPPORTED' section.

How to assert a function was called with specific arguments in Mock?

Use `assert_called` with exact values or pattern matchers like `:meck.is/1` for advanced validation, as demonstrated in the README with struct matching and custom logic.

Is Mock compatible with async ExUnit tests?

No, you must set `async: false` in test modules using Mock to avoid conflicts, as mocking has global effects that prevent parallel test execution.

How to mock a function that returns different values on repeated calls?

Use the `in_series` option in the mock definition to specify a series of return values for consecutive calls, though the README cautions this is only for rare stateful scenarios.

mock — Elixir Mocking Library

What is mock?

Mock is a mocking library for the Elixir programming language that enables developers to create mock modules for testing purposes. It leverages the Erlang meck library and provides convenient Elixir macros to integrate mocking functionality seamlessly into test suites, allowing developers to isolate and test code with external dependencies.

Target Audience

Elixir developers writing unit and integration tests who need to mock external dependencies like HTTP clients, databases, or third-party APIs. It is particularly useful for developers working on test suites that require controlled environments to verify interactions with external modules.

Value Proposition

Developers choose Mock because it offers a clean, Elixir-native interface to the underlying Erlang meck library, making it easier to write and maintain tests with mocks. Its macros like `with_mock` and `test_with_mock` simplify test setup, and features like partial mocking with `:passthrough` and advanced assertion helpers provide flexibility and clarity in test code.

Mocking library for Elixir language

Use Cases

Best For

Testing Elixir applications that interact with external HTTP APIs by mocking HTTP client modules like HTTPotion.
Isolating database interactions in unit tests by mocking Ecto or database adapter modules.
Verifying function call patterns and frequencies in tests using assertion helpers like `assert_called` and `assert_called_exactly`.
Mocking multiple modules simultaneously in a single test with the `with_mocks` macro for complex dependency scenarios.
Partially mocking modules where only specific functions need to be mocked while others remain functional using the `:passthrough` option.
Creating mock functions that return different values based on input patterns, useful for simulating varied responses from external services.

Not Ideal For

Projects requiring asynchronous test execution with mocks, as Mock forces `async: false` due to global effects
Teams needing to mock internal function calls without refactoring code to use fully qualified names
Developers looking to mock macros directly, as Mock requires wrapper function workarounds
Applications that demand fine-grained mock behaviors beyond module-level replacement, where libraries like Mox might be more suitable

Pros & Cons

Pros

Clean Macro API

Offers Elixir-native macros like `with_mock` and `test_with_mock` that integrate seamlessly into ExUnit tests, simplifying mock setup and improving code readability as shown in the README examples.

Flexible Assertion Helpers

Provides a range of assertion macros such as `assert_called` with wildcard and pattern matching support via `:meck.is/1`, enabling precise verification of function calls without manual checks.

Partial Mocking Support

Includes the `:passthrough` option to mock specific functions while allowing access to other functions in the module, useful for isolating dependencies without full module replacement.

Input-Dependent Mocks

Allows defining mock functions with multiple clauses to return different values based on input patterns, making it easy to simulate varied responses from external services.

Cons

No Internal Call Mocking

Cannot mock functions called internally within the same module without refactoring to use fully qualified names, a limitation explicitly admitted in the README's 'NOT SUPPORTED' section.

Async Test Incompatibility

Mocking modules cannot be done asynchronously, requiring tests to run with `async: false`, which slows down test suites and limits parallelism in larger projects.

Macro Mocking Unsupported

Does not support mocking macros directly, forcing developers to create wrapper functions as a workaround, adding unnecessary complexity and boilerplate to tests.

Frequently Asked Questions

What is mock?

Target Audience

Value Proposition

Use Cases

Best For

Testing Elixir applications that interact with external HTTP APIs by mocking HTTP client modules like HTTPotion.
Isolating database interactions in unit tests by mocking Ecto or database adapter modules.
Verifying function call patterns and frequencies in tests using assertion helpers like `assert_called` and `assert_called_exactly`.
Mocking multiple modules simultaneously in a single test with the `with_mocks` macro for complex dependency scenarios.
Partially mocking modules where only specific functions need to be mocked while others remain functional using the `:passthrough` option.
Creating mock functions that return different values based on input patterns, useful for simulating varied responses from external services.

Not Ideal For

Projects requiring asynchronous test execution with mocks, as Mock forces `async: false` due to global effects
Teams needing to mock internal function calls without refactoring code to use fully qualified names
Developers looking to mock macros directly, as Mock requires wrapper function workarounds
Applications that demand fine-grained mock behaviors beyond module-level replacement, where libraries like Mox might be more suitable

Pros & Cons

Pros

Clean Macro API

Offers Elixir-native macros like `with_mock` and `test_with_mock` that integrate seamlessly into ExUnit tests, simplifying mock setup and improving code readability as shown in the README examples.

Flexible Assertion Helpers

Provides a range of assertion macros such as `assert_called` with wildcard and pattern matching support via `:meck.is/1`, enabling precise verification of function calls without manual checks.

Partial Mocking Support

Includes the `:passthrough` option to mock specific functions while allowing access to other functions in the module, useful for isolating dependencies without full module replacement.

Input-Dependent Mocks

Allows defining mock functions with multiple clauses to return different values based on input patterns, making it easy to simulate varied responses from external services.

Cons

No Internal Call Mocking

Cannot mock functions called internally within the same module without refactoring to use fully qualified names, a limitation explicitly admitted in the README's 'NOT SUPPORTED' section.

Async Test Incompatibility

Mocking modules cannot be done asynchronously, requiring tests to run with `async: false`, which slows down test suites and limits parallelism in larger projects.

Macro Mocking Unsupported

Does not support mocking macros directly, forcing developers to create wrapper functions as a workaround, adding unnecessary complexity and boilerplate to tests.

Frequently Asked Questions

mock

What is mock?

Overview

Use Cases

Best For

Not Ideal For

Pros & Cons

Pros

Cons

Frequently Asked Questions

Related Projects

Found a gem we're missing?

mock

What is mock?

Overview

Use Cases

Best For

Not Ideal For

Pros & Cons

Pros

Cons

Frequently Asked Questions

Related Projects

Found a gem we're missing?