Mocking stubbing

Skill ulpi-io/plugin-marketplace/plugins/aj-geddes/skills/mocking-stubbing

A curated collection of 7,800+ agent skills for Claude Desktop, sourced from skills.sh

Install

npx -y skills add ulpi-io/plugin-marketplace --skill mocking-stubbing

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

2 things to look at

no licenseNo license file was found in the repository. Code published without one is not open source by default, so using it at work is a question for whoever answers licensing questions where you are.
1 stars1 stars. Stars are a popularity signal and not a quality one, but at this level it is likely that nobody has read this closely except its author, and you would be relying on your own review.

What its author says it does

Copied from the file, not written here

Create and manage mocks, stubs, spies, and test doubles for isolating unit tests from external dependencies. Use for mock, stub, spy, test double, Mockito, Jest mocks, and dependency isolation.

SKILL.md

3.1 KB, as published. Nobody here has run it

Overview

Mocking and stubbing are essential techniques for isolating units of code during testing by replacing dependencies with controlled test doubles. This enables fast, reliable, and focused unit tests that don't depend on external systems like databases, APIs, or file systems.

When to Use

Isolating unit tests from external dependencies
Testing code that depends on slow operations (DB, network)
Simulating error conditions and edge cases
Verifying interactions between objects
Testing code with non-deterministic behavior (time, randomness)
Avoiding expensive operations in tests
Testing error handling without triggering real failures

Quick Start

Minimal working example:

// services/UserService.ts
import { UserRepository } from "./UserRepository";
import { EmailService } from "./EmailService";

export class UserService {
  constructor(
    private userRepository: UserRepository,
    private emailService: EmailService,
  ) {}

  async createUser(userData: CreateUserDto) {
    const user = await this.userRepository.create(userData);
    await this.emailService.sendWelcomeEmail(user.email, user.name);
    return user;
  }

  async getUserStats(userId: string) {
    const user = await this.userRepository.findById(userId);
    if (!user) throw new Error("User not found");

    const orderCount = await this.userRepository.getOrderCount(userId);
    return { ...user, orderCount };
  }
}

// ... (see reference guides for full implementation)

Reference Guides

Detailed implementations in the references/ directory:

Guide	Contents
Jest Mocking (JavaScript/TypeScript)	Jest Mocking (JavaScript/TypeScript)
Python Mocking with unittest.mock	Python Mocking with unittest.mock
Mockito for Java	Mockito for Java
Advanced Mocking Patterns	Advanced Mocking Patterns

Best Practices

✅ DO

Mock external dependencies (DB, API, file system)
Use dependency injection for easier mocking
Verify important interactions with mocks
Reset mocks between tests
Mock at the boundary (repositories, services)
Use spies for partial mocking when needed
Create reusable mock factories
Test both success and failure scenarios

❌ DON'T

Mock everything (don't mock what you own)
Over-specify mock interactions
Use mocks in integration tests
Mock simple utility functions
Create complex mock hierarchies
Forget to verify mock calls
Share mocks between tests
Mock just to make tests pass