Abstract:Existing approaches to microservice dependency simulation--record-replay, pattern-mining, and specification-driven stubs--generate static artifacts before test execution. These artifacts can only reproduce behaviors encoded at generation time; on error-handling and code-reasoning scenarios, which are underrepresented in typical trace corpora, record-replay achieves 0% and 12% fidelity in our evaluation.
We propose online LLM simulation, a runtime approach where the LLM answers each dependency request as it arrives, maintaining cross-request state throughout a test scenario. The model reads the dependency's source code, caller code, and production traces, then simulates behavior on demand--trading latency (~3 s per request) and cost ($0.16-$0.82 per dependency) for coverage on scenarios that static artifacts miss.
We instantiate this approach in MIRAGE and evaluate it on 110 test scenarios across three microservice systems (Google's Online Boutique, Weaveworks' Sock Shop, and a custom system). In white-box mode, MIRAGE achieves 99% status-code and 99% response-shape fidelity, compared to 62% / 16% for record-replay. A signal ablation shows dependency source code is often sufficient (100% alone); without it, the model retains error-code accuracy (94%) but loses response-structure fidelity (75%). Results are stable across three LLM families (within 3%) and deterministic across repeated runs. Caller integration tests produce the same pass/fail outcomes with MIRAGE as with real dependencies (8/8 scenarios).
From: Xinran Zhang [view email]
[v1]
Mon, 6 Apr 2026 16:10:23 UTC (51 KB)
[v2]
Tue, 7 Apr 2026 02:14:17 UTC (47 KB)
[v3]
Sun, 12 Apr 2026 05:46:58 UTC (51 KB)
[v4]
Fri, 26 Jun 2026 04:41:35 UTC (121 KB)
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