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Ownership, testing, and flag cleanup

Flags are production branches. When temporary flags outlive their purpose, tests multiply and nobody knows which path is real.

Healthy flag metadata​

Every flag needs a key, purpose, type, packaged default, accountable owner, creation/expiry dates, removal ticket, affected clients, dependencies, success metric, guardrails, and rollback signal. Reject “mobile team” as owner when nobody is on the hook during an incident.

Test the policy, not the SDK​

class FakeFlags(private val values: Map<Flag<Boolean>, Boolean>) : FlagReader {
    override fun isEnabled(flag: Flag<Boolean>) = values[flag] ?: flag.default
}

@Test fun `off uses legacy checkout`() {
    val policy = CheckoutPolicy(FakeFlags(mapOf(Flag.NewCheckout to false)))
    assertFalse(policy.useNewFlow())
}

@Test fun `on uses new checkout`() {
    val policy = CheckoutPolicy(FakeFlags(mapOf(Flag.NewCheckout to true)))
    assertTrue(policy.useNewFlow())
}

Also test changes before entry, during a journey, process death, stale cache, malformed data, offline operation, and logout.

Combination explosion​

Ten Booleans create 1,024 combinations. Keep decisions independent, reject invalid combinations, exhaustively test high-risk domain states, use pairwise/risk-based integration coverage, and smoke-test production defaults. Avoid high-cardinality telemetry for every combination.

Complete removal​

  1. Freeze the winning value and observe it.
  2. Make the branch unconditional and delete the loser/tests.
  3. Keep compatible server config while old installed versions need it.
  4. Remove targeting, analytics, dashboards, documentation, and runbooks.
  5. Verify Android, iOS, web, and backend no longer read the key.

Automate owner/expiry lint, pre-expiry alerts, stale 0%/100% reports, and cross-repository key search.

Practical mistakes​

  • ❌ Test only the future “on” branch.
  • ✅ Test both branches and transitions until deletion.
  • ❌ Nest many raw flag reads inside a composable.
  • ✅ Resolve one domain policy and render its state.
  • ❌ Recycle an old key for a new meaning.
  • ✅ Use a versioned key; old clients and analytics retain history.
  • ❌ Delete server configuration immediately at 100%.
  • ✅ Plan for old app versions still in use.

Exercise​

Audit five flags. Record classification, owner, default, age, rollout, downstream consumers, and exact deletion steps. Estimate the branches removed.