How to Mock a Remote Config Fetch in Python

Simulate a remote config API response with metadata, timestamps, and mock data for testing or local development.

Easy Python 3.9+ Aug 9, 2026 A/B testing & experimentation 14 views 0 copies

mock config testing experimentation fixture

Python code

22 lines

Python 3.9+

import json
from datetime import datetime
from typing import Any, Dict

def fetch_remote_config(mock_data: Dict[str, Any]) -> Dict[str, Any]:
    """Simulate fetching a remote config with metadata and timestamps."""
    return {
        "status": "success",
        "source": "mock",
        "fetched_at": datetime.utcnow().isoformat(),
        "config": mock_data
    }

if __name__ == "__main__":
    mock_config = {
        "feature_flag": True,
        "timeout_seconds": 30,
        "service_url": "https://api.example.com",
        "max_retries": 3
    }
    result = fetch_remote_config(mock_config)
    print(json.dumps(result, indent=2))

Output

stdout

{
  "status": "success",
  "source": "mock",
  "fetched_at": "2025-01-15T10:30:45.123456",
  "config": {
    "feature_flag": true,
    "timeout_seconds": 30,
    "service_url": "https://api.example.com",
    "max_retries": 3
  }
}

How it works

The fetch_remote_config function wraps the mock data in a structured envelope that mimics a real remote config API response. The datetime.utcnow().isoformat() adds an ISO-8601 timestamp, making the output look like a live fetch. The nested config key preserves the original mock dictionary so callers can access the configuration values directly. This pattern is useful for development, testing, and A/B experimentation when a real backend isn't available or shouldn't be hit repeatedly.

Common mistakes

Forgetting to add the metadata fields (status, source, fetched_at) that real APIs include
Using `datetime.utcnow()` which is deprecated in Python 3.12+ — prefer `datetime.now(timezone.utc)`
Not handling the case where the mock dict may contain nested data or non-serializable types

Variations

Add latency simulation with `time.sleep(random.uniform(0.1, 0.5))` before returning
Read mock config from a JSON file instead of hardcoding it in the script
Use `functools.lru_cache` to cache the fetched config for repeated calls

Real-world use cases

Local development where the real config service isn't reachable or is rate-limited.
Unit testing feature-flag logic without making network calls to the production config service.
A/B experiment rollouts where teams need a deterministic config baseline before traffic ramps up.

How to Mock a Remote Config Fetch in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

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Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from A/B testing & experimentation

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Tutorials

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