ADR-073: First-party test doubles for consumer-facing interfaces 

Context 

The feature-service interfaces are documented as the consumer entry points (ADR-051): a downstream extension depends on ToolCallingServiceInterface or EmbeddingServiceInterface and, in its own unit tests, substitutes a fake. Every consumer currently hand-rolls that fake. nr_ai_search carries a FakeToolCallingService and a FakeEmbeddingService under its own test namespace, re-deriving the canned-response and call-recording behaviour that any consumer of the same interface needs.

A hand-rolled fake also re-introduces the maintenance trap ADR-051 set out to remove: it drifts from the interface it imitates. When the interface grows a method the fake does not implement, the consumer's suite fatals — the same breakage that blocked nr_ai_search's 0.13 → 0.16 update.

Decision 

Ship maintained test doubles from nr_llm itself, in a new runtime-autoloaded namespace Netresearch\NrLlm\Testing\ (Classes/Testing/, mapped by the production autoload block, not autoload-dev) so consumers autoload them without nr_llm's dev dependencies:

• FakeToolCallingService implements ToolCallingServiceInterface: a FIFO queue of CompletionResponse values, per-call recording for both methods, and a settable throwable.
• FakeEmbeddingService implements EmbeddingServiceInterface: canned vectors plus per-call recording for the five provider-backed embed* methods (so a test can assert the LlmConfiguration was passed through) and canned returns for the four pure vector helpers, which a fake has no reason to reimplement.

Both implement the real interface, so PHPStan fails the build if a fake drifts from the contract — the drift ADR-051 could not prevent for a consumer's own copy is now caught here.

The fakes are excluded from container autoconfiguration (Classes/Testing/* in the Configuration/Services.yaml exclude list) and add no public: true override, so the audited public-service count (ADR-028 / ADR-065 / ADR-069) is unchanged. Their docblocks mark them as consumer test fixtures, not for production wiring.

Consequences 

• A consumer deletes its hand-rolled fake and type-hints Netresearch\NrLlm\Testing\Fake* instead; the double tracks the interface automatically.
• The Testing\ namespace is a supported public surface. Renaming a fake's properties or methods is a breaking change for consumers and belongs in a release note.
• The fakes cover the tool-calling and embedding interfaces named in ADR-051. Other feature interfaces (completion, vision, translation) gain a first-party fake only when a consumer needs one.