Write Unit Test

Write Unit Test

Purpose

Convert functional specifications into executable test code. Tests define the behavioral contract that the implementation must satisfy, following Test-Driven Development principles.

When to Use

This skill should be used when:

• User provides functional specifications with Preconditions/Workflow/Postconditions structure
• User requests to "write tests" or "implement tests" for a spec
• Starting TDD workflow (tests first, implementation later)
• User says "create tests for this spec"

Functional Specification Format

Specs follow a three-part structure for each scenario:

Preconditions: Initial database state (CSV-like format)

table_name:
column1, column2, column3
value1, value2, value3

Workflow: Bullet points describing the sequence of actions

* Call `class.method(args)`
* [What happens internally]
* Returns [object type]

Postconditions: Expected database state after execution (includes pre-existing + new rows)

table_name:
column1, column2, column3, column4
value1, value2, value3, newvalue

Use placeholders for runtime-generated values: <uuid>, <timestamp>, <vector>, <1536-dim vector>

Test Generation Workflow

1. Parse the Specification

For each scenario in the spec:

• Extract test name from scenario title (convert to "should [action] when [condition]" format)
• Identify all tables and their initial states from Preconditions
• Extract the method call from the first Workflow bullet
• Identify expected return values and database state from Postconditions

2. Generate Test File Structure

Create test file at [module]/tests/[class-name].test.ts:

import { describe, it, expect, beforeEach } from 'vitest';
import { PreDB, PostDB } from '@/lib/b-test';
import { db } from '@/db';
import * as schema from '@/db/schema';
import { ClassName } from '@/path/to/class';

describe('ClassName', () => {
  let instance: ClassName;

  beforeEach(() => {
    instance = new ClassName(db);
  });

  const TEST_TIMEOUT = 120000; // For API calls

  it('[test name]', async () => {
    // PreDB: Setup
    await PreDB(db, schema, { /* ... */ });

    // Execute
    const result = await instance.method();

    // Assertions
    expect(result.field).toBe(expectedValue);

    // PostDB: Verify
    await PostDB(db, schema, { /* ... */ }, { allowExtraRows: true });
  }, TEST_TIMEOUT);
});

3. Translation Rules

Preconditions → PreDB:

• Empty tables: table: []
• With data: Map CSV rows to objects with proper types
• Timestamps: Use const now = new Date()
• Vectors: Use new Array(1536).fill(0.1) for test data

Workflow → Execution:

• First bullet indicates the public method to call
• Only call the public method, not internal implementation details
• Add comment describing what the method does conceptually

Postconditions → Assertions + PostDB:

• Derive assertions from expected values (types, ranges, specific values)
• Use allowExtraRows: true when pre-existing rows exist
• Only verify the new/changed data, reference actual result values

4. Complete All Scenarios

Generate one it() block per scenario in the specification. Include all scenarios to ensure comprehensive test coverage.

5. Report to User

Show the generated test file and explain:

• Tests will fail initially (no implementation yet)
• Tests define the contract for what needs to be implemented
• Tests document expected behavior

Key Principles

TDD Philosophy:

• Tests are written BEFORE implementation exists
• Expected outcome: tests fail initially (red), then implementation makes them pass (green)
• Tests define the contract, not validate existing code

Testing Approach:

• Test behavior (what happens), not implementation (how it works)
• Use real database operations and real API calls (no mocks)
• Make tests readable with clear sections (PreDB, Execute, Verify)
• Use descriptive test names

Avoid:

• Mocks, spies, or stubs
• Testing private methods or internal state
• .toHaveBeenCalledWith() assertions
• Hardcoding generated values like UUIDs in assertions

Reference Materials

For detailed translation rules, complete examples, and common patterns, refer to:

• references/translation-guide.md: Comprehensive spec-to-test examples, placeholder handling, multi-table scenarios, and best practices

Required Context

Before generating tests, ensure access to:

1. The functional specification (Preconditions/Workflow/Postconditions)
2. The class/module name and import path
3. The database schema location (db/schema.ts)
4. Knowledge of which tables are involved

If any are missing, ask the user for clarification before proceeding.