testland/flagsmith-testing
Wraps Flagsmith server-side SDK testing patterns (feature flags / feature toggles) so tests run without calling the Flagsmith API: offline mode with LocalFileHandler + a downloaded environment.json snapshot, local-evaluation mode (no per-request network), and default_flag_handler for per-feature mocked fallbacks, via the get_environment_flags / get_identity_flags evaluation paths. Use when writing feature-flag tests for code that uses Flagsmith, mocking flag values, or testing feature toggles offline in CI.
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flagsmith-modes.mdreferences/
Flagsmith test modes, anti-patterns, and limitations
Deeper detail for flagsmith-testing. Offline mode (covered in the skill spine) is the default for tests; the modes below are secondary.
Local-evaluation mode
Polls the Flagsmith API periodically and evaluates flags locally between refreshes (no per-request network, but not zero network):
flagsmith = Flagsmith(
environment_key="server-key",
enable_local_evaluation=True,
environment_refresh_interval_seconds=60,
)Local mode polls; offline mode does not. For tests, offline is usually preferred.
default_flag_handler - per-flag mock
Programmatic fallback used when the offline environment.json
does not have the flag under test yet:
from flagsmith import Flagsmith
from flagsmith.models import DefaultFlag
def default_flag_handler(feature_name: str) -> DefaultFlag:
if feature_name == "secret_button":
return DefaultFlag(enabled=False, value='{"colour": "#b8b8b8"}')
return DefaultFlag(enabled=False, value=None)
flagsmith = Flagsmith(
environment_key="test-key",
default_flag_handler=default_flag_handler,
)Useful when the offline environment.json does not have the flag you are testing yet.
Anti-patterns
| Anti-pattern | Why it fails | Fix |
|---|---|---|
| Production env_key in tests | Real API calls + analytics pollution | offline_mode + LocalFileHandler |
| environment.json not committed | Test flakes when prod changes | Commit; refresh deliberately |
| Mixing offline_mode + local_evaluation_mode | Conflicting; one takes precedence | Pick one |
| default_flag_handler returns DefaultFlag with no value | Tests for value-based flags fail silently | Always set value |
Skipping flagsmith.get_identity_flags for identity-scoped tests | Bypasses per-user logic | Use identity API |
| Per-test new Flagsmith client | Slow init | Session-scoped fixture |
Limitations
- environment.json is point-in-time. Drift invisible.
- default_flag_handler only fires for missing flags in local-eval mode. In offline mode it can be used for fallback.
- No granular per-user override API. Use traits + segments via the environment.json.
- Doesn't validate Flagsmith's own logic. Platform-side evaluation is separate.