Unit Test Generator

Overview

Unit Test Generator takes the tedium out of writing tests without sacrificing quality. Point it at a function, class, or module, and it generates a comprehensive test suite that covers happy paths, edge cases, error conditions, and boundary values.

This isn’t template-based test generation. The skill understands your code’s semantics — it knows when a function can throw, what inputs cause edge cases, and how to properly mock dependencies. Tests follow your project’s existing patterns and use your preferred testing framework.

Whether you’re backfilling tests for legacy code or generating tests alongside new features, Unit Test Generator dramatically accelerates your testing workflow.

How It Works

1. Parse — Analyzes the target code, its dependencies, and existing test patterns in your project
2. Plan — Identifies all testable behaviors, edge cases, and error paths
3. Generate — Creates test files using your project’s testing framework (Jest, pytest, JUnit, etc.)
4. Validate — Runs the generated tests to ensure they pass and provide meaningful coverage

Use Cases

• Legacy code coverage — Backfill tests for untested code before refactoring
• TDD acceleration — Generate test stubs from function signatures before implementation
• Edge case discovery — Find boundary conditions and error paths you might miss
• Refactoring safety net — Generate comprehensive tests before making structural changes
• CI/CD gates — Ensure minimum coverage thresholds are met

Getting Started

# Using Claude Code
claude "Generate unit tests for src/services/auth.ts"

# Or via CLI
test-gen generate --file src/services/auth.ts --framework jest

Example

For a function like:

function divide(a: number, b: number): number {
  if (b === 0) throw new Error("Division by zero");
  return a / b;
}

Generated tests:

describe("divide", () => {
  it("divides two positive numbers", () => {
    expect(divide(10, 2)).toBe(5);
  });

  it("handles negative numbers", () => {
    expect(divide(-10, 2)).toBe(-5);
  });

  it("throws on division by zero", () => {
    expect(() => divide(10, 0)).toThrow("Division by zero");
  });

  it("handles floating point division", () => {
    expect(divide(1, 3)).toBeCloseTo(0.333, 2);
  });
});

Alternatives

• Copilot Test Generation — GitHub Copilot’s built-in test suggestion
• Diffblue Cover — Java-focused unit test generation
• CodiumAI — AI test generation with behavior analysis