Patch
Patch - Ergonomic Mocking for Elixir
Patch makes it easy to replace functionality in tests with test specific functionality. Patch augments ExUnit with several utilities that make writing tests in Elixir fast and easy. Patch includes unique functionality that no other mocking library for Elixir provides, Patch's Super Powers.
Features
Why use Patch instead of meck, Mock, Mockery, Mox, etc?
Patch starts with a very simple idea for how a patched function should work.
Patched functions should always return the mock value they are given.
Here are the key features of Patch.
- Easy-to-use and composable interface with sensible defaults.
- First class support for working with Processes.
- No testing code in non-test code.
In addition to these features which many libraries aspire to, Patch has 3 additional features that no other mocking library for Elixir / Erlang seem to have. These Super Powers are
- Patch mocks are effective for both local and remote calls. This means a patched function always resolves to the patch.
- Patch can patch private functions without changing their visibility.
- Patch makes it possible to test your private functions without changing their visibility via the
expose/2functionality.
See the Mockompare companion project for a comparison of Elixir / Erlang mocking libraries. If there is a way to accomplish the following with another library, please open an issue so this section and the comparisons can be updated.
For more information about Patch's Super Powers see the Super Powers Documentation
Table of Contents
Installation
Add patch to your mix.exs
def deps do
[
{:patch, "~> 0.12.0", only: [:test]}
]
endQuickstart
After adding the dependency just add the following line to any test module after using your test case
use PatchThis library comes with a comprehensive suite of unit tests. These tests not only verify that the library is working correctly but are designed so that for every bit of functionality there is an easy to understand example for how to use that feature. Check out the User Tests for examples of how to use each feature.
Using Patch adds 11 core functions, 10 assertions, 7 mock value builders, and 1 utility function to the test.
See the Cheatsheet for an overview of how the library can be used and as a handy reference. Continue below for links to more in-depth documentation including the Guidebook.
Core Functions
Core functions let us apply patches, patch processes, intercept messages, and query our patched modules.
| Core Function | Description |
|---|---|
| expose/2 | Expose private functions as public for the purposes of testing |
| fake/2 | Replaces a module with a fake module |
| history/1,2 | Returns the call history for a mock |
| inject/3,4 | Injects a listener into a GenServer |
| listen/3 | Intercepts messages to a process and forwards them to the test process |
| patch/3 | Patches a function so that it returns a mock value |
| private/1 | Macro to call exposed private functions without raising a compiler warning |
| real/1 | Resolves the real module for a patched module |
| replace/3 | Replaces part of the state of a GenServer |
| restore/1,2 | Restores an entire module or just a function within a module to its pre-patched form |
| spy/1 | Patches a module so calls can be asserted without changing behavior |
Assertions
Assertions make it easy to assert that a patched module has or has not observed a call.
| Assertion | Description |
|---|---|
| assert_any_call/1 | Asserts that any call of any arity has occurred on the mocked module for a function name (preferred macro) |
| assert_any_call/2 | Asserts that any call of any arity has occurred on the mocked module for a function name (advanced use cases) |
| assert_called/1 | Asserts that a particular call has occurred on a mocked module |
| assert_called/2 | Asserts that a particular call has occurred a given number of times on a mocked module |
| assert_called_once/1 | Asserts that a particular call has occurred exactly once on a mocked module |
| refute_any_call/1 | Refutes that any call of any arity has occurred on the mocked module for a function name (preferred macro) |
| refute_any_call/2 | Refutes that any call of any arity has occurred on the mocked module for a function name (advanced use cases) |
| refute_called/1 | Refutes that a particular call has occurred on a mocked module |
| refute_called/2 | Refutes that a particular call has occurred a given number of time on a mocked module |
| refute_called_once/1 | Refutes that a particular call has occurred exactly once on a mocked module |
Value Builders
Patched functions aren't limited to only returning simple scalar values, a host of Value Builders are provided for all kinds of testing scenarios. See the patch documentation for details.
| Value Builder | Description |
|---|---|
| callable/1,2 | Callable that will be invoked on every patch invocation, dispatch and evaluation modes can be customized |
| cycle/1 | Cycles through the values provided on every invocation |
| raises/1 | Raises a RuntimeException with the given message upon invocation |
| raises/2 | Raises the specified Exception with the given attribtues upon invocation |
| scalar/1 | Returns the argument as a literal, useful for returning functions |
| sequence/1 | Returns the values in order, repeating the last value indefinitely |
| throws/1 | Throws the given value upon invocation |
Utility Functions
Patch comes with some utilities that can assist when tests aren't behaving as expected.
| Utility Function | Description |
|---|---|
| debug/0,1 | Enable or Disable debug mode for a given test |
Guide Book
Patch comes with plenty of documentation and a Suite of User Tests that show how to use the library.
For a guided tour and deep dive of Patch, see the Guide Book
Support Matrix
Tests automatically run against a matrix of OTP and Elixir Versions, see the ci.yml for details.
| OTP \ Elixir | 1.7 | 1.8 | 1.9 | 1.10 | 1.11 | 1.12 | 1.13 | 1.14 |
|---|---|---|---|---|---|---|---|---|
| 20 | β | β | β | N/A | N/A | N/A | N/A | N/A |
| 21 | β | β | β | β | β | N/A | N/A | N/A |
| 22 | β | β | β | β | β | β | β | N/A |
| 23 | N/A | N/A | N/A | β | β | β | β | β |
| 24 | N/A | N/A | N/A | N/A | β | β | β | β |
| 25 | N/A | N/A | N/A | N/A | N/A | N/A | β | β |
Limitations
Patch works by recompiling modules, this alters the global execution environment.
Since the global execution environment is altered by Patch, Patch is not compatible with async: true.
Prior Art
Up to version 0.5.0 Patch was based off the excellent meck library. Patch Super Powers required a custom replacement for meck, Patch.Mock.
Patch also takes inspiration from python's unittest.mock.patch for API design.
Contributors
Patch is made better everyday by developers requesting new features.
- daisyzhou
- Suggested the new function pass through behavior introduced in v0.9.0
- likeanocean
- Suggested
assert_called/2,assert_called_once/1,refute_called/2, andrefute_called_once/1introduced in v0.7.0
- Suggested
- birarda
- Suggested
assert_any_call/2,refute_any_call/2introduced in v0.2.0
- Suggested
- kianmeng
- Corrected several typographical errata
- Dorgan
- Reported erratum in the Patch Cheatsheet
If you have a suggestion for improvements to this library, please open an issue.
Changelog
See the Changelog