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testland/feature-flag-test-harness

Use when a feature behind a flag must be tested both on and off, or several flags interact. Runs the same suite under the minimum set of flag combinations with an OpenFeature in-memory provider, as labeled CI matrix shards, and reports results per combination.

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Provider wiring - OpenFeature in-memory provider

Per openfeature-providers, "Providers are responsible for performing flag evaluations" - the in-memory test provider returns the flag values the test wants.

Node / TypeScript

// tests/harness/flag-harness.ts
import { OpenFeature, InMemoryProvider } from '@openfeature/server-sdk';

export function withFlags(flags: Record<string, unknown>) {
  const provider = new InMemoryProvider(
    Object.fromEntries(
      Object.entries(flags).map(([k, v]) => [k, {
        defaultVariant: 'configured',
        variants: { configured: v },
        disabled: false,
      }]),
    ),
  );
  return OpenFeature.setProviderAndWait(provider);
}

Then in the test setup:

import { withFlags } from './harness/flag-harness';

beforeAll(async () => {
  await withFlags(JSON.parse(process.env.FLAGS_JSON || '{}'));
});

Python

# tests/harness/flag_harness.py
from openfeature.api import set_provider
from openfeature.provider.in_memory_provider import InMemoryProvider, InMemoryFlag

def with_flags(flags: dict):
    set_provider(InMemoryProvider({
        k: InMemoryFlag(default_variant='configured',
                        variants={'configured': v})
        for k, v in flags.items()
    }))

Java

import dev.openfeature.sdk.OpenFeatureAPI;
import dev.openfeature.contrib.providers.memory.InMemoryProvider;

@BeforeAll
static void wireFlags() {
    var flags = parseEnv(System.getenv("FLAGS_JSON"));  // your JSON parser
    OpenFeatureAPI.getInstance().setProvider(new InMemoryProvider(flags));
}

Evaluation API

The application code calls the standard OpenFeature evaluation API (openfeature-eval):

const client = OpenFeature.getClient();
const enabled = await client.getBooleanValue('new_checkout', false);

Per openfeature-eval: "the default value must also be specified ... In the case of any error during flag evaluation, the default value will be returned, so give consideration to your default values!" The harness picks the value the in-memory provider returns; the application's hard-coded default is what runs in prod-flag-failure scenarios.