Agent skill

condition-based-waiting

Use when tests have race conditions, timing dependencies, or inconsistent pass/fail behavior - replaces arbitrary timeouts with condition polling to wait for actual state changes, eliminating flaky tests from timing guesses

View SKILL.md on GitHub Repository
Stars 1
Forks 0

Install this agent skill to your Project

npx add-skill https://github.com/ljchg12-hue/dotfiles/tree/main/skills/superpowers/skills/condition-based-waiting

SKILL.md

Condition-Based Waiting

Overview

Flaky tests often guess at timing with arbitrary delays. This creates race conditions where tests pass on fast machines but fail under load or in CI.

Core principle: Wait for the actual condition you care about, not a guess about how long it takes.

When to Use

dot
digraph when_to_use {
    "Test uses setTimeout/sleep?" [shape=diamond];
    "Testing timing behavior?" [shape=diamond];
    "Document WHY timeout needed" [shape=box];
    "Use condition-based waiting" [shape=box];

    "Test uses setTimeout/sleep?" -> "Testing timing behavior?" [label="yes"];
    "Testing timing behavior?" -> "Document WHY timeout needed" [label="yes"];
    "Testing timing behavior?" -> "Use condition-based waiting" [label="no"];
}

Use when:

  • Tests have arbitrary delays (setTimeout, sleep, time.sleep())
  • Tests are flaky (pass sometimes, fail under load)
  • Tests timeout when run in parallel
  • Waiting for async operations to complete

Don't use when:

  • Testing actual timing behavior (debounce, throttle intervals)
  • Always document WHY if using arbitrary timeout

Core Pattern

typescript
// ❌ BEFORE: Guessing at timing
await new Promise(r => setTimeout(r, 50));
const result = getResult();
expect(result).toBeDefined();

// ✅ AFTER: Waiting for condition
await waitFor(() => getResult() !== undefined);
const result = getResult();
expect(result).toBeDefined();

Quick Patterns

Scenario Pattern
Wait for event waitFor(() => events.find(e => e.type === 'DONE'))
Wait for state waitFor(() => machine.state === 'ready')
Wait for count waitFor(() => items.length >= 5)
Wait for file waitFor(() => fs.existsSync(path))
Complex condition waitFor(() => obj.ready && obj.value > 10)

Implementation

Generic polling function:

typescript
async function waitFor<T>(
  condition: () => T | undefined | null | false,
  description: string,
  timeoutMs = 5000
): Promise<T> {
  const startTime = Date.now();

  while (true) {
    const result = condition();
    if (result) return result;

    if (Date.now() - startTime > timeoutMs) {
      throw new Error(`Timeout waiting for ${description} after ${timeoutMs}ms`);
    }

    await new Promise(r => setTimeout(r, 10)); // Poll every 10ms
  }
}

See @example.ts for complete implementation with domain-specific helpers (waitForEvent, waitForEventCount, waitForEventMatch) from actual debugging session.

Common Mistakes

❌ Polling too fast: setTimeout(check, 1) - wastes CPU ✅ Fix: Poll every 10ms

❌ No timeout: Loop forever if condition never met ✅ Fix: Always include timeout with clear error

❌ Stale data: Cache state before loop ✅ Fix: Call getter inside loop for fresh data

When Arbitrary Timeout IS Correct

typescript
// Tool ticks every 100ms - need 2 ticks to verify partial output
await waitForEvent(manager, 'TOOL_STARTED'); // First: wait for condition
await new Promise(r => setTimeout(r, 200));   // Then: wait for timed behavior
// 200ms = 2 ticks at 100ms intervals - documented and justified

Requirements:

  1. First wait for triggering condition
  2. Based on known timing (not guessing)
  3. Comment explaining WHY

Real-World Impact

From debugging session (2025-10-03):

  • Fixed 15 flaky tests across 3 files
  • Pass rate: 60% → 100%
  • Execution time: 40% faster
  • No more race conditions

Recommended Agent Skills

Expand your agent's capabilities with these related and highly-rated skills.

ljchg12-hue/dotfiles

random-selection

Randomly select items from lists using various algorithms for fair and unbiased selection

1 0
Explore
ljchg12-hue/dotfiles

threat-hunting

Proactive threat detection using Sigma rules, IOCs, and behavioral analytics

1 0
Explore
ljchg12-hue/dotfiles

auth-implementation-patterns

Master authentication and authorization patterns including JWT, OAuth2, session management, and RBAC to build secure, scalable access control systems. Use when implementing auth systems, securing APIs, or debugging security issues.

1 0
Explore
ljchg12-hue/dotfiles

debugging-strategies

Master systematic debugging techniques, profiling tools, and root cause analysis to efficiently track down bugs across any codebase or technology stack. Use when investigating bugs, performance issues, or unexpected behavior.

1 0
Explore
ljchg12-hue/dotfiles

sql-optimization-patterns

Master SQL query optimization, indexing strategies, and EXPLAIN analysis to dramatically improve database performance and eliminate slow queries. Use when debugging slow queries, designing database schemas, or optimizing application performance.

1 0
Explore
ljchg12-hue/dotfiles

monorepo-management

Master monorepo management with Turborepo, Nx, and pnpm workspaces to build efficient, scalable multi-package repositories with optimized builds and dependency management. Use when setting up monorepos, optimizing builds, or managing shared dependencies.

1 0
Explore

Didn't find tool you were looking for?

Be as detailed as possible for better results