How do I ensure a mock function is called exactly once?

The skill demonstrates how to use the .times(1) expectation on your mock objects to enforce strict call counting during test execution.

Does this support custom argument matching logic?

Yes, it provides guidance on using predicates, including the ability to pass custom closures to validate that function arguments meet specific criteria.

Can I mock async functions with this skill?

Yes, it includes specific implementation patterns for mocking asynchronous traits, which is essential for modern Rust applications using runtimes like Tokio.

What library does this skill use for mocking in Rust?

This skill focuses on using 'mockall', the most popular and feature-complete mocking library for the Rust programming language.

Is trait-based design required for this mocking approach?

While mockall can mock some concrete types, the best practice encouraged by this skill is using trait-based abstractions to decouple your code for maximum testability.

Rust Mocking & Unit Testing

Name: Rust Mocking & Unit Testing
Author: gar-ai

bygar-ai

•

Security & Testing

Simplifies Rust unit testing by generating mock implementations for traits and external dependencies using the mockall crate.

This skill enables Claude to architect highly testable Rust applications through trait-based abstractions and the mockall framework. It provides comprehensive patterns for setting up mock expectations, handling asynchronous traits, and verifying complex interaction sequences. By guiding developers to isolate business logic from external side effects like databases or APIs, this skill helps create robust, isolated unit tests that run quickly and reliably without requiring live infrastructure.

Key Features

01Advanced argument matching using predicates like eq, range, and custom functions

021 GitHub stars

03Automatic mock generation using the #[automock] attribute

04Support for mocking asynchronous traits with async-trait compatibility

05Strict call counting and verification to ensure expected code paths are executed

06Sequence enforcement for validating the order of operations in complex workflows

Use Cases

01Simulating network failures and edge-case error returns in a controlled environment

02Isolating business logic from database repositories or external API clients

03Testing generic components by mocking traits with specific type parameters

What are Skills?·How to Install

Install with 🐟 Skill.Fish

npx skillfish add gar-ai/mallorn rust-testing-mocking

For use in Claude.ai and ChatGPT

Download Skill