Ephemeral E2E Browser Testing

The Problem

Running Cypress or Playwright tests locally is painful. Your test suite either:

• Destroys your development database state (dropped tables, truncated records)
• Fights active ports causing cryptic connection refusals mid-test
• Requires manual reset scripts you have to remember to run before and after

The Solution: devx test ui

devx test ui boots an entirely clean, isolated topology just for your tests — fresh databases on random ports, completely separate from your active development environment. When the tests finish, everything is torn down automatically. Your dev DB is never touched.

devx test ui --command "npx playwright test"

Configuration

CLI + YAML Parity: All options are configurable both via CLI flags and devx.yaml. Neither is a second-class citizen.

YAML Configuration (committed team defaults)

# devx.yaml
name: my-app

databases:
  - engine: postgres
  - engine: redis

test:
  ui:
    setup: "npm run db:migrate"    # Run before tests (migrations, seeds, etc.)
    command: "npx playwright test" # The test runner command

CLI Flags (one-off use, overrides YAML)

# Simplest form — reads everything from devx.yaml
devx test ui

# Override the test command inline
devx test ui --command "npx playwright test"

# Add a setup (migration) step
devx test ui --setup "npm run db:migrate" --command "npx playwright test"

# Pass arguments directly after -- 
devx test ui -- npx playwright test --reporter=html

# Use Docker instead of Podman
devx test ui --runtime docker --command "npx playwright test"

How It Works

1. Generates a unique run ID (e.g., 698e02) to namespace all ephemeral resources
2. Provisions isolated containers for each database in devx.yaml, each bound to a random free port
3. Waits for readiness by polling container logs for the database startup marker
4. Injects environment variables into the test process:
   • DATABASE_URL — the first database's connection string (primary)
   • <ENGINE>_URL — per-engine URLs (e.g., POSTGRES_URL, REDIS_URL)
5. Runs setup (e.g., migrations) with the injected environment
6. Runs the test command
7. Tears down all containers and volumes unconditionally on exit — whether tests pass, fail, or crash

Environment Variables Injected

Variable	Example Value	Description
DATABASE_URL	postgresql://devx:devx@localhost:59785/devx	Primary database connection
POSTGRES_URL	postgresql://devx:devx@localhost:59785/devx	PostgreSQL-specific URL
REDIS_URL	redis://localhost:59822	Redis-specific URL

Verification Proof

The test run below demonstrates a full lifecycle: two fresh databases are booted on dynamic ports, the test receives the correct injected DATABASE_URL, and both containers are destroyed cleanly on exit — the primary development database remains completely untouched.

Pre-processing

The setup step is designed for idempotent migration commands like npm run prisma db push or npm run db:migrate. These same steps should mirror your deployment pipeline to shift pre-processing validation left and catch issues early.

Single engine instance per type

devx test ui currently provisions one ephemeral container per engine type (mirroring devx db spawn). Multi-instance support (e.g. two separate Postgres databases) is a future enhancement.