How to Test Both Flag States in CI With a Matrix

A matrix over the flag value runs the suite with the flag on and off, so neither path regresses silently.

While a flag exists, both states are live code. A GitHub Actions matrix that sets the flag to on and off runs the whole suite against each, catching breakage in either branch.

Steps

Read the flag override from an environment variable in tests.
Add a matrix dimension with the flag values on and off.
Set the env var from matrix.flag so each leg forces one state.

Matrix over the flag

.github/workflows/ci.yml

jobs:
  test:
    runs-on: ubuntu-latest
    strategy:
      matrix:
        flag: [on, off]
    env:
      FF_NEW_CHECKOUT: ${{ matrix.flag }}
    steps:
      - uses: actions/checkout@v4
      - run: npm ci && npm test

Honor the override in code

Terminal

function newCheckoutEnabled() {
  const override = process.env.FF_NEW_CHECKOUT;
  if (override) return override === 'on';
  return flags.getBooleanValue('new-checkout', false);
}

Gotchas

Only override in test builds; a leaked override in production defeats the real flag.
Two states double the run count, so keep flags short-lived to bound the matrix.