VCSDD Language Profile: TypeScript

Verification Toolset

Tier	Tool	Install	Use Case
1	fast-check	npm install -D fast-check	Property-based testing
1	@stryker-mutator/core	npm install -D @stryker-mutator/core	Mutation testing
1	vitest / jest	npm install -D vitest	Unit + property tests

fast-check Pattern

import * as fc from 'fast-check';
import { describe, it } from 'vitest';
import { parse, serialize } from '../src/parser';

describe('parser properties', () => {
  it('never throws on arbitrary input', () => {
    fc.assert(
      fc.property(fc.string(), (s) => {
        // Should return Ok or Err, never throw
        const result = parse(s);
        return result !== undefined;
      })
    );
  });

  it('roundtrip: parse(serialize(x)) === x', () => {
    fc.assert(
      fc.property(fc.string({ minLength: 1, maxLength: 50 }), (s) => {
        const result = parse(s);
        if (result.ok) {
          return serialize(result.value) === s;
        }
        return true; // Error cases are valid
      }),
      { numRuns: 1000 }
    );
  });
});

Stryker Setup

# Initialize Stryker
npx stryker init

# Run mutation testing
npx stryker run

# Check results in reports/mutation/

stryker.config.js:

module.exports = {
  mutate: ['src/**/*.ts', '!src/**/*.test.ts'],
  testRunner: 'vitest',
  reporters: ['html', 'clear-text', 'progress'],
  thresholds: { high: 80, low: 60, break: 50 },
};

Type-Safe Result Pattern

type Result<T, E> = { ok: true; value: T } | { ok: false; error: E };

function parse(input: string): Result<ParsedDoc, ParseError> {
  if (!input) return { ok: false, error: ParseError.Empty };
  // ...
}

Using discriminated unions ensures the compiler enforces error handling.