PostHog CI Integration

Overview

Set up CI/CD pipelines for PostHog integrations. Covers mocked unit tests (no API key needed), integration tests against a PostHog dev project, and deployment annotations that mark releases in your PostHog timeline.

Prerequisites

• GitHub repository with Actions enabled
• PostHog dev project API key for integration tests
• PostHog personal API key for deployment annotations
• npm/pnpm project with vitest or jest

Instructions

Step 1: Configure GitHub Secrets

set -euo pipefail
# Project key for integration tests (phc_... from dev project)
gh secret set POSTHOG_TEST_KEY --body "phc_dev_project_key"

# Personal key for deployment annotations (phx_...)
gh secret set POSTHOG_PERSONAL_API_KEY --body "phx_your_personal_key"

# Project ID for annotations
gh secret set POSTHOG_PROJECT_ID --body "12345"

Step 2: GitHub Actions Workflow

# .github/workflows/posthog-tests.yml
name: PostHog Tests

on:
  push:
    branches: [main]
  pull_request:
    branches: [main]

jobs:
  unit-tests:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: '20'
          cache: 'npm'
      - run: npm ci
      - run: npm test -- --coverage
        # Unit tests use mocked PostHog — no API key needed

  integration-tests:
    runs-on: ubuntu-latest
    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
    needs: unit-tests
    env:
      NEXT_PUBLIC_POSTHOG_KEY: ${{ secrets.POSTHOG_TEST_KEY }}
      POSTHOG_HOST: https://us.i.posthog.com
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-node@v4
        with:
          node-version: '20'
          cache: 'npm'
      - run: npm ci
      - run: npm run test:integration
        timeout-minutes: 5

  annotate-deploy:
    runs-on: ubuntu-latest
    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
    needs: integration-tests
    steps:
      - name: Create PostHog annotation
        env:
          POSTHOG_PERSONAL_API_KEY: ${{ secrets.POSTHOG_PERSONAL_API_KEY }}
          POSTHOG_PROJECT_ID: ${{ secrets.POSTHOG_PROJECT_ID }}
        run: |
          curl -X POST "https://app.posthog.com/api/projects/$POSTHOG_PROJECT_ID/annotations/" \
            -H "Authorization: Bearer $POSTHOG_PERSONAL_API_KEY" \
            -H "Content-Type: application/json" \
            -d "{
              \"content\": \"Deploy: ${GITHUB_SHA::8} — ${GITHUB_EVENT_HEAD_COMMIT_MESSAGE:-$(git log -1 --pretty=%s)}\",
              \"date_marker\": \"$(date -u +%Y-%m-%dT%H:%M:%SZ)\",
              \"scope\": \"project\"
            }"

Step 3: Unit Tests with Mocked PostHog

// tests/analytics.test.ts — runs in CI without any API keys
import { describe, it, expect, vi, beforeEach } from 'vitest';

vi.mock('posthog-node', () => ({
  PostHog: vi.fn().mockImplementation(() => ({
    capture: vi.fn(),
    identify: vi.fn(),
    getFeatureFlag: vi.fn().mockResolvedValue('control'),
    isFeatureEnabled: vi.fn().mockResolvedValue(true),
    getAllFlags: vi.fn().mockResolvedValue({ 'new-feature': true }),
    flush: vi.fn().mockResolvedValue(undefined),
    shutdown: vi.fn().mockResolvedValue(undefined),
  })),
}));

import { PostHog } from 'posthog-node';

describe('PostHog Analytics', () => {
  let ph: InstanceType<typeof PostHog>;

  beforeEach(() => {
    vi.clearAllMocks();
    ph = new PostHog('phc_test');
  });

  it('captures events with required properties', () => {
    ph.capture({
      distinctId: 'user-1',
      event: 'subscription_started',
      properties: { plan: 'pro', interval: 'annual' },
    });

    expect(ph.capture).toHaveBeenCalledWith(
      expect.objectContaining({
        event: 'subscription_started',
        properties: expect.objectContaining({ plan: 'pro' }),
      })
    );
  });

  it('evaluates feature flags with default fallback', async () => {
    const enabled = await ph.isFeatureEnabled('new-feature', 'user-1');
    expect(enabled).toBe(true);
  });

  it('gets multivariate flag variant', async () => {
    const variant = await ph.getFeatureFlag('experiment', 'user-1');
    expect(variant).toBe('control');
  });
});

Step 4: Integration Tests (Real PostHog Project)

// tests/integration/posthog.test.ts
import { describe, it, expect, afterAll } from 'vitest';
import { PostHog } from 'posthog-node';

const KEY = process.env.NEXT_PUBLIC_POSTHOG_KEY;

describe.skipIf(!KEY)('PostHog Integration', () => {
  const ph = new PostHog(KEY!, {
    host: process.env.POSTHOG_HOST || 'https://us.i.posthog.com',
    flushAt: 1,
    flushInterval: 0,
  });

  afterAll(async () => await ph.shutdown());

  it('captures and flushes an event', async () => {
    ph.capture({
      distinctId: `ci-${Date.now()}`,
      event: 'ci_integration_test',
      properties: {
        ci: true,
        run_id: process.env.GITHUB_RUN_ID || 'local',
      },
    });
    await expect(ph.flush()).resolves.not.toThrow();
  });

  it('evaluates feature flags', async () => {
    const flags = await ph.getAllFlags(`ci-${Date.now()}`);
    expect(typeof flags).toBe('object');
  });

  it('resolves decide endpoint', async () => {
    const response = await fetch('https://us.i.posthog.com/decide/?v=3', {
      method: 'POST',
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ api_key: KEY, distinct_id: 'ci-test' }),
    });
    expect(response.status).toBe(200);
    const data = await response.json();
    expect(data).toHaveProperty('featureFlags');
  });
});

Step 5: Package Scripts

{
  "scripts": {
    "test": "vitest run",
    "test:integration": "vitest run tests/integration/",
    "test:coverage": "vitest run --coverage"
  }
}

Error Handling

Output

• Unit test suite with mocked PostHog (runs everywhere, no keys needed)
• Integration test suite against PostHog dev project (runs on main only)
• Deployment annotations marking each release in PostHog timeline
• GitHub Actions workflow with proper secret management

Resources

• GitHub Actions Secrets
• PostHog Annotations API
• Vitest Documentation

Next Steps

For deployment patterns, see posthog-deploy-integration.