condition-based-waiting

name	Condition-Based Waiting
description	Replace arbitrary timeouts with condition polling for reliable async tests
when_to_use	when tests have race conditions, timing dependencies, or inconsistent pass/fail behavior
version	1.1.0
languages	all
progressive_disclosure	{"entry_point":{"summary":"Replace arbitrary timeouts with condition polling for reliable async tests","when_to_use":"Tests with setTimeout/sleep, flaky tests, or timing-dependent async operations","quick_start":"1. Identify arbitrary delays in tests (setTimeout, sleep, time.sleep())\n2. Replace with condition-based waiting (waitFor pattern)\n3. Use domain-specific helpers for common scenarios\nSee @example.ts for complete working implementation\n","core_pattern":"// ❌ Guessing at timing\nawait new Promise(r => setTimeout(r, 50));\n\n// ✅ Waiting for condition\nawait waitFor(() => getResult() !== undefined);\n"},"references":[{"path":"references/patterns-and-implementation.md","purpose":"Detailed waiting patterns, implementation guide, and common mistakes","when_to_read":"When implementing waitFor or debugging timing issues"}]}
effort	medium

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

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

// ❌ 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