10.8ADR-008: Parallel Test Execution

Context

Running tests sequentially is slow. But browser tests have shared state issues.

Decision

• Sequential by default in development (one reused session)
• Parallel via named sessions — each worker gets its own isolated session (-s=worker-N), which the CLI keeps separate in the .playwright-cli/ workspace
• Parallel limit: match available CPU cores (each browser instance uses ~200MB RAM + 1 core)

# Parallel execution (4 workers), one named session per test
cat test_list.txt | xargs -P4 -I{} bash -c '
  ./run-single-test.sh "{}"      # script opens/closes session -s="{}"
'

Constraints

• Each parallel worker needs its own browser instance (~200MB RAM)
• 8-core CI machine: max ~6 parallel workers (leave 2 cores for OS + agent)
• Network-bound tests may not benefit from parallelism