First-time evaluator: How do I even test if an integration will work?

You're overthinking it. Start with a controlled, observable test before you write a single line of integration logic.

First, isolate the endpoints. Use `curl` or a simple script to verify the API contract matches the docs. Capture the exact request/response.

```bash
curl -X POST https://their-api.com/v1/webhook
-H "Content-Type: application/json"
-H "Authorization: Bearer $TEST_KEY"
-d '{"test_event": "ping"}'
-v > response.log 2>&1
```

Key metrics to baseline:
* Latency from your test client to their API.
* Status codes for both happy and error paths.
* Exact JSON schema of the response.

Then, simulate the integration flow locally. Use a mock server to mimic their webhook callbacks to your system. Tools like `nc` or `python -m http.server` can verify you can even receive traffic.

```python
# Quick mock endpoint to validate payload
from http.server import HTTPServer, BaseHTTPRequestHandler
import json

class Handler(BaseHTTPRequestHandler):
def do_POST(self):
length = int(self.headers.get('Content-Length'))
body = self.rfile.read(length)
print(json.loads(body)) # Inspect what they actually send
self.send_response(200)
self.end_headers()

HTTPServer(('localhost', 8001), Handler).serve_forever()
```

If this works, you've proven the network path and basic compatibility. Only then should you build the actual integration. Most failures happen at this basic layer—timeouts, auth issues, or schema mismatches.