testland/unleash-testing

Wraps Unleash (Open Source / SaaS) SDK testing patterns: bootstrap with a static toggles array (no network), the test mode (disableMetrics + disablePolling), the custom strategy testing pattern (implement a Strategy class + assert isEnabled), and assignment-integrity tests. Use when writing tests for code that uses Unleash for feature flags.

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name:: unleash-testing
description:: Wraps Unleash (Open Source / SaaS) SDK testing patterns: bootstrap with a static toggles array (no network), the test mode (disableMetrics + disablePolling), the custom strategy testing pattern (implement a Strategy class + assert isEnabled), and assignment-integrity tests. Use when writing tests for code that uses Unleash for feature flags.

unleash-testing

Name: testland/unleash-testing
Rating: 80 (1 reviews)
Author: testland

When to use

Tests for code that calls unleash.isEnabled(flagName, context).
Tests for custom Unleash strategies (the extensibility point).
Assignment-integrity tests per ab-test-validity-checklist.

Authoring

Install

npm install --save-dev unleash-client
pip install UnleashClient

Bootstrap with toggles (offline)

import { initialize } from 'unleash-client';

const unleash = initialize({
  url: 'http://localhost:4242/api/',
  appName: 'test-app',
  disableMetrics: true,        // No metrics upload
  disablePolling: true,        // No background polling
  bootstrap: {
    data: [
      {
        name: 'show-new-ui',
        enabled: true,
        strategies: [
          { name: 'default' },
        ],
      },
    ],
  },
});

// Wait for initialization
await new Promise<void>((resolve) => unleash.once('synchronized', resolve));

The bootstrap.data array is the SDK's initial flag state; since polling is disabled, that state persists for the test session.

isEnabled tests

test('flag enabled', () => {
  expect(unleash.isEnabled('show-new-ui')).toBe(true);
});

test('flag with context', () => {
  expect(unleash.isEnabled('premium-only', { userId: 'u1', properties: { tier: 'premium' } })).toBe(true);
});

Custom strategy

Unleash's extensibility: custom strategies implement an isEnabled(parameters, context) method.

import { Strategy } from 'unleash-client';

class TenantStrategy extends Strategy {
  constructor() { super('tenantStrategy'); }
  isEnabled(parameters: any, context: any): boolean {
    const allowedTenants = (parameters.tenants ?? '').split(',');
    return allowedTenants.includes(context.tenantId);
  }
}

const unleash = initialize({
  url: '...',
  appName: 'test',
  strategies: [new TenantStrategy()],
  bootstrap: {
    data: [
      {
        name: 'flag-x',
        enabled: true,
        strategies: [{ name: 'tenantStrategy', parameters: { tenants: 'A,B' } }],
      },
    ],
  },
});

test('strategy allows tenant A', () => {
  expect(unleash.isEnabled('flag-x', { tenantId: 'A' })).toBe(true);
});

test('strategy rejects tenant C', () => {
  expect(unleash.isEnabled('flag-x', { tenantId: 'C' })).toBe(false);
});

Percentage-rollout determinism

const unleash = initialize({
  // ...
  bootstrap: {
    data: [
      {
        name: 'gradual-rollout',
        enabled: true,
        strategies: [{ name: 'flexibleRollout', parameters: { rollout: '50', stickiness: 'userId' } }],
      },
    ],
  },
});

test('rollout deterministic per user', () => {
  const r1 = unleash.isEnabled('gradual-rollout', { userId: 'u1' });
  const r2 = unleash.isEnabled('gradual-rollout', { userId: 'u1' });
  expect(r1).toBe(r2);
});

Teardown

afterAll(() => unleash.destroy());

Running

npm test

CI integration

jobs:
  unleash-tests:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v5
      - uses: actions/setup-node@v4
      - run: npm ci && npm test

Fully offline - no Unleash server URL needed since polling is disabled.

Anti-patterns

Anti-pattern	Why it fails	Fix
`disableMetrics: false` in CI	Spurious metrics POSTs	Always `disableMetrics: true` in tests
`disablePolling: false` without test-only URL	Network calls; CI flakes	Always disable polling in offline tests
`bootstrap.data` is stale	Drift from prod definitions	Pull from Unleash periodically; commit fixture
Custom strategies not unit-tested	Logic bugs in the strategy itself	Test the strategy class in isolation too
Skipping `synchronized` event wait	Race: isEnabled returns default	Always await synchronized
Forgetting `unleash.destroy()`	Goroutine / timer leak	Always destroy in afterAll
Tests use real Unleash server	Slow; flaky if server down	Bootstrap mode

Limitations

Bootstrap is point-in-time. Drift between fixture + Unleash UI is invisible.
Custom strategies tested in isolation lose context. Integration test with the full SDK still needed.
Metric-side tests need real server. If you're testing the metrics export path, bootstrap mode is wrong.
Stickiness is parameter-driven. A misconfigured stickiness parameter shows up in production, not in tests.

References

Unleash docs: docs.getunleash.io.
Node SDK: docs.getunleash.io/sdks/node.
Custom strategies: docs.getunleash.io/concepts/activation-strategies.
Companion: feature-flag-test-matrix-reference.
Sibling SDKs: launchdarkly-testing, flagsmith-testing, growthbook-testing.

Workspace: testland
Visibility: Public
Created: 8 days ago
Last updated: 7 days ago
Repository: https://github.com/testland/qa
Publish Source: GitHub
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