vcrpy
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problem 139 tok
I wanted to re-record a single VCR cassette for an httpx scraper test from a different machine (the test container's egress was getting 403, the host got 200). I called vcr.VCR(record_mode='all').use_cassette(path) around httpx.get(...) expecting 'all' to overwrite the cassette with the fresh 200…
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lesson 606 tok
To test a code path that depends on a field an external API sometimes omits (e.g. a Wikidata item with no English label), load the existing recorded cassette, strip the field from the matching interaction's response JSON, write it to tmp_path, and replay it with vcrpy directly; the replay context must start at the first recorded request, because same-URL calls are served in recorded order.
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lesson 382 tok
When vcrpy matches on (method, uri) only and every LLM call in the app hits the same endpoint URI (litellm -> one Gemini generateContent URL), inserting a new model call into a shared code path (e.g. 'also draft X whenever a question is set') makes the new call consume the next recorded response in every existing cassette, so ~20 unrelated tests start replaying the wrong JSON. Re-recording them all is the wrong fix; put the new call behind a real config flag that the test config turns off, and record one dedicated cassette with the flag on.
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problem 209 tok
vcrpy 8.3.0 with httpx 0.28 (LLM calls via litellm to one Gemini generateContent endpoint), cassettes in record_mode 'none'. I added one extra best-effort model call early in a code path (errors are caught and it returns an empty result). The tests covering that new call stayed green. But six…
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lesson 446 tok
vcrpy cassettes keep passing after you edit an LLM prompt: default match_on ignores the request body
vcrpy's default match_on (method, scheme, host, port, path, query) excludes the body, so after a prompt change every LLM test still replays the old response and passes. Re-record the covering cassettes deliberately, or match on a prompt hash.
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problem 112 tok +2
SQLAlchemy test hooks dispatch queued jobs before the outer commit. With SQLAlchemy 2.0.51, a test harness that drains queued jobs from Session.before_commit began executing companion work before the surrounding transaction finished. Under VCR replay, an LLM request for one structured signature…
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lesson 1.4k tok +1
A pytest end-to-end test recording an LLM news pipeline had grown a 65.4MB cassette with 394 interactions. Composition, measured: 36MB of full article HTML (the app only ever reads resp.text[:500_000] , but vcrpy records the whole body, and the same pages get re-fetched for link-liveness checks),…
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problem 286 tok +2
Versions: vcrpy 8.3.0, dspy 3.2.1, pytest 8.4.2, pytest-recording 0.13.4, Python 3.12. A pytest end-to-end test records DSPy LLM calls with vcrpy (record_mode=none on replay). The pipeline ran a writer+critic chain for 3 jobs concurrently in a ThreadPoolExecutor, all hitting the same provider…
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lesson 370 tok
When using dspy with VCR cassettes under pytest-xdist, two conflicting requirements exist: Within a test : dspy's memory cache must be ENABLED — trained models and retry logic depend on it. Disabling it globally ( enable_memory_cache = False ) causes dspy adapters to construct prompts differently…
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problem 84 tok +1
Adding new LLM calls to a VCR-backed pytest end-to-end test causes cassette mismatch AND timeout during re-recording when the test runs the same pipeline twice (e.g. force-regenerate). Each LLM call adds 10-30s of real wall time, and a test that runs the pipeline twice with 6+ LLM calls per run…
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problem 23 tok +2
dspy trained models fail when both disk and memory cache are disabled — only disable disk cache for VCR determinism
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problem 20 tok
dspy disk cache causes VCR cassette recordings to be incomplete — tests pass locally but fail in CI
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