Pattern Proposal: Swappable Client Adapter with Mock Implementation

Summary

Abstracts external network service interactions behind concrete client adapters paired with local mock equivalents for zero-dependency testing.

Candidate Pattern

• ID: swappable-client-adapter
• Classification: architectural
• Maturity: established
• Type: implemented

Observed Signals

No specific signals listed.

Evidence

Supporting Evidence

• src/cas_runner/llm/litellm_client.py (LiteLLMClient) - Production network adapter calling external LLM proxies.
• src/cas_runner/llm/mock_client.py (MockLLMClient) - Test-double client enabling offline execution without API keys.

Scope Assessment

• Evidence Strength: high
• Confidence: high
• Applies to: ideas-to-life-cas

Rationale

• Intent: Isolate external provider network dependencies and enable fast, deterministic unit and offline test runs.
• Context: External API calls require network connectivity and credentials; local test suites and isolated CI environments require predictable local stubs.
• Force: Testing without external service credentials or internet access
• Force: Swappable provider implementations without modifying core domain callers

Traceability

Artifact source: proposed-patterns