Pattern Proposal: Client Adapter and Test Double

Summary

Separates real external network/API communication from test environments via symmetric client interfaces.

Candidate Pattern

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

Observed Signals

No specific signals listed.

Evidence

Supporting Evidence

• src/cas_runner/llm/litellm_client.py (LiteLLMClient) - Production adapter calling external LiteLLM APIs.
• src/cas_runner/llm/mock_client.py (MockLLMClient) - Offline test double providing stubbed or simulated responses.

Scope Assessment

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

Rationale

• Intent: Allow offline execution, deterministic testing, and CI validation without calling live external provider APIs.
• Context: External integrations (such as LiteLLM API providers) are costly, non-deterministic, or unavailable during local builds and unit tests.
• Force: Components requiring provider interaction must execute without active internet connections or credentials
• Force: Mock implementations must adhere to the identical call interface as real clients

Traceability

Artifact source: proposed-patterns