Pytest VCR Workflow

Use this skill when recording or re-recording VCR cassettes for tests, or when debugging cassette contents.

Prerequisites

• Verify .env exists: test -f .env && echo 'ok' || echo 'missing'
• Missing API keys will cause clear test errors at runtime

Important flags

• --record-mode=rewrite : Record cassettes (works for both new and existing)
• --lf : Run only the last failed tests
• -vv : Verbose output
• --tb=line : Short traceback output
• -k="" : Run tests matching the given substring expression

Recording Cassettes

Step 1: Record cassettes

source .env && uv run pytest path/to/test.py::test_function_name -v --tb=line --record-mode=rewrite

Multiple tests can be specified:

source .env && uv run pytest path/to/test.py::test_one path/to/test.py::test_two -v --tb=line --record-mode=rewrite

Step 2: Verify recordings

Run the same tests WITHOUT --record-mode to verify cassettes play back correctly:

source .env && uv run pytest path/to/test.py::test_function_name -vv --tb=line

Step 3: Review snapshots

If tests use snapshot() assertions:

• The test run in Step 2 auto-fills snapshot content
• Review the generated snapshot files to ensure they match expected output
• You only review - don't manually write snapshot contents
• Snapshots capture what the test actually produced, additional to explicit assertions

Parsing Cassettes

Parse VCR cassette YAML files to inspect request/response bodies without dealing with raw YAML.

Usage

uv run python .claude/skills/testing-skill/parse_cassette.py <cassette_path> [--interaction N]

Examples

# Parse all interactions in a cassette
uv run python .claude/skills/testing-skill/parse_cassette.py tests/models/cassettes/test_foo/test_bar.yaml

# Parse only interaction 1 (0-indexed)
uv run python .claude/skills/testing-skill/parse_cassette.py tests/models/cassettes/test_foo/test_bar.yaml --interaction 1

Output

For each interaction, shows:

• Request: method, URI, parsed body (truncated base64)
• Response: status code, parsed body (truncated base64)

Base64 strings longer than 100 chars are truncated for readability.

Full Workflow Example

# 1. Record cassette
source .env && uv run pytest tests/models/test_openai.py::test_chat_completion -v --tb=line --record-mode=rewrite

# 2. Verify playback and fill snapshots
source .env && uv run pytest tests/models/test_openai.py::test_chat_completion -vv --tb=line

# 3. Review test code diffs (excludes cassettes)
git diff tests/ -- ':!**/cassettes/**'

# 4. List new/changed cassettes (name only - use parse_cassette.py to inspect)
git diff --name-only tests/ -- '**/cassettes/**'

# 5. Inspect cassette contents if needed
uv run python .claude/skills/testing-skill/parse_cassette.py tests/models/cassettes/test_openai/test_chat_completion.yaml