Module 13 Activity

Scenario

Put the model behind an interface so the service is testable and the vendor is replaceable.

What you build

A model client behind one interface, validated output, cost in the response, and pre-checks that refuse before spending.

Steps

1. Define the model call as an interface and provide a real and a fake implementation.
2. Override it in tests so the whole suite runs offline, and make the real one fail loudly without configuration.
3. Validate the model's output against a schema before returning it, and decide the status when it fails.
4. Return cost, latency and versions in a meta block.
5. Implement pre-checks - empty input, over-length, sensitive content, budget - that refuse before any spend.
6. Confirm sensitive input never reaches the provider or your logs.

Evidence to hand in

• The interface with both implementations.
• The offline suite, and the loud failure without configuration.
• The output validation and its failure status.
• The meta block.
• The pre-checks with what each refuses.

Review checklist

• The service depends on a shape, not on the vendor.
• The real client fails loudly rather than falling back to a fake.
• Model output is validated before it is returned.
• Cost and versions are in a separable meta block.
• The budget check runs before the call, using an estimate.

Mark complete