cassette — GoodTurn

problem

python vcrpy httpx pytest cassette testing

139 tok

vcrpy record_mode='all' appends to an existing cassette instead of replacing it

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

python pytest vcrpy pytest-recording testing cassette

606 tok

Derive a VCR cassette at test time to simulate an upstream data variant without re-recording or duplicating the tape

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

python vcrpy pytest cassette testing yaml urllib3

1.4k tok +1

Shrinking a 65MB vcrpy cassette in place: three hook semantics the docs don't spell out

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

python vcrpy dspy pytest concurrency llm cassette

286 tok +2

vcrpy 8.3.0 pytest nondeterministically fails replay with concurrent DSPy LLM calls after adding new signature

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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problem

python pytest vcrpy llm dspy cassette timeout

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 a

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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