Test-Driven Development

Write a failing test first. Then write only enough code to make it pass. No exceptions.

The Iron Law

NO IMPLEMENTATION BEFORE A FAILING TEST.

Write code before a test? Delete it. Start over.

No exceptions:

• Not for "trivial" functions
• Not for "obvious" logic
• Not for bug fixes ("I just need to change one line")
• Don't keep it as "reference" while writing tests
• Delete means delete

RED-GREEN-REFACTOR

RED   → Write test → run → watch it FAIL (required)
GREEN → Write minimal code → run → watch it PASS
REFACTOR → Clean up → run → still passes

Never skip RED. A test that passes without you writing any implementation is not a TDD test.

Rust (src-tauri)

Test location: inline #[cfg(test)] module at the bottom of the same .rs file.

Commands:

# Run all tests
cd asyar-launcher/src-tauri && cargo test

# Run tests for one file/module
cargo test <module_name>

# See output from passing tests too
cargo test -- --nocapture

Pattern:

pub fn some_function(input: &str) -> Result<String, AppError> {
    // ← implement AFTER tests are written and failing
    todo!()
}

#[cfg(test)]
mod tests {
    use super::*;

    // Step 1: Write this first, run cargo test, watch it fail
    #[test]
    fn test_some_function_happy_path() {
        let result = some_function("valid input").unwrap();
        assert_eq!(result, "expected output");
    }

    #[test]
    fn test_some_function_error_case() {
        let result = some_function("");
        assert!(result.is_err());
    }

    // Use factory helpers for complex types
    fn make_test_manifest(id: &str) -> ExtensionManifest {
        ExtensionManifest { id: id.to_string(), ..Default::default() }
    }
}

TypeScript / Svelte 5 (src)

Test location: colocated *.test.ts file (e.g. src/services/foo/FooService.test.ts).

Commands:

cd asyar-launcher

# Watch mode during development
pnpm test

# Single run (CI / verify before done)
pnpm test:run

Pattern:

// Step 1: Write this file first, run pnpm test:run, watch it fail
import { describe, it, expect, vi, beforeEach } from 'vitest';

// Mock dependencies BEFORE importing the module under test
vi.mock('@tauri-apps/api/core', () => ({ invoke: vi.fn() }));
vi.mock('../log/logService', () => ({
  logService: { debug: vi.fn(), info: vi.fn(), warn: vi.fn(), error: vi.fn() },
}));

// Import AFTER mocks are declared
import { FooService } from './FooService';
import { invoke } from '@tauri-apps/api/core';

describe('FooService', () => {
  beforeEach(() => vi.clearAllMocks());

  it('calls invoke with correct command', async () => {
    vi.mocked(invoke).mockResolvedValueOnce({ id: '1', name: 'Test' });

    const result = await FooService.getItem('1');

    expect(invoke).toHaveBeenCalledWith('get_item', { id: '1' });
    expect(result.name).toBe('Test');
  });

  it('throws on invoke error', async () => {
    vi.mocked(invoke).mockRejectedValueOnce(new Error('not found'));
    await expect(FooService.getItem('missing')).rejects.toThrow('not found');
  });
});

Cross-Module & Registry Integration Tests

Unit tests with heavy mocking often hide multi-module bugs (e.g. duplicate action IDs, conflicting registrations across ActionService and ExtensionLoader).

When a feature interacts across registration boundaries:

1. Write an integration test that boots the real modules together (e.g. ExtensionLoader registering manifest actions into ActionService).
2. Assert that no duplicate IDs, duplicate shortcuts, or clashing UI labels are produced in the shared registry.

Quick Reference

Task	Command	Location
Run Rust tests	cargo test (in src-tauri/)	*.rs inline #[cfg(test)]
Run launcher TS tests (watch)	pnpm test (in asyar-launcher/)	src/**/*.test.ts
Run launcher TS tests (once)	pnpm test:run (in asyar-launcher/)	src/**/*.test.ts
Run SDK tests (once)	pnpm test:run (in asyar-sdk/)	src/**/*.test.ts
Mock Tauri invoke	vi.mock('@tauri-apps/api/core', ...)	top of test file
Mock globals/env	vi.stubGlobal() / vi.stubEnv()	inside test, restore in afterEach

Common Mistakes

Mistake	Fix
Writing implementation first	Delete it. Write test first.
Test passes without implementation	You wrote the wrong test. It must fail first.
Forgetting vi.mock() hoisting	Declare vi.mock() before any imports
Not clearing mocks	Add beforeEach(() => vi.clearAllMocks())
Testing in Svelte component directly	Extract logic to .ts file, test that
Not running cargo test after Rust changes	Always verify: cd src-tauri && cargo test

Red Flags — STOP and Start Over

• "I'll write the test after, it's a small change"
• "This is just a refactor, tests aren't needed"
• "The bug fix is obvious, I don't need a test"
• "I already know it works"
• "Let me just implement it and then add the test"

All of these mean: write the test first. No exceptions.