Testing Roadmap: unit standards, VCR integration, contract drift, data validation gates

[SatoryKono]

Summary

Track practical testing improvements as a parent roadmap rather than treating
this issue as a single implementation ticket.

Why

The repository already benefits more from smaller executable child issues than
from one large testing umbrella. This issue should remain the coordination
layer for the testing roadmap.

Purpose

Parent roadmap for testing governance tracks. Execution should happen in child
issues.

Tracks

1. Unit Test Standards

• Define expectations for pure transformation logic and high-signal unit
  coverage
• Improve coverage in the most valuable areas first
• Keep edge-case expectations explicit

2. Integration and VCR Policy

• Tighten conventions for integration and e2e coverage
• Keep fixture and cassette governance explicit
• Keep local and CI execution paths aligned

3. Contract Drift Checks

• Add focused external provider drift checks where risk is meaningful
• Prefer small, readable checks over a broad framework rollout

4. Data Validation Gates

• Define where Pandera or equivalent validation belongs in the quality model
• Add small, high-signal gates incrementally

Out of Scope

• Delivering the entire testing strategy in one issue
• Blanket enforcement across the whole repository from one ticket
• Immediate rollout of every possible testing framework

Coordination Checklist

• Unit standards track has an executable child issue or completed
  implementation note
• Integration/VCR policy track is tracked in a child issue
• Contract drift track is tracked in a child issue
• Data validation gates track is tracked in a child issue
• Parent issue links current child issues and marks completed ones
• Parent body clearly distinguishes roadmap tracking from active
  implementation

Notes

This issue should stay open only as a coordination/meta artifact.

Concrete work should happen in smaller scoped child issues with explicit
acceptance criteria and bounded blast radius.

Related

• Links to child issues should be maintained here as the roadmap evolves

[SatoryKono]

Retriaged from a broad strategy umbrella into a phased execution roadmap. Concrete follow-up work should now be split and delivered incrementally instead of keeping the entire testing platform vision in one issue.

[SatoryKono]

Split the testing roadmap into executable child issues so the parent can stay roadmap-shaped while implementation moves in smaller slices.

Created or confirmed child issues:

• Unit Test Standards Baseline for Pure Transformation Logic #2597 Unit Test Standards Baseline for Pure Transformation Logic
  Scope: Unit-test baseline for pure transformation logic, focused on determinism and edge-case coverage.
• Integration and VCR Policy Tightening for Supported Pipelines #2598 Integration and VCR Policy Tightening for Supported Pipelines
  Scope: Integration, e2e, and VCR policy tightening for supported pipeline families.
• Provider Contract Drift Checks MVP for External Schemas and Fields #2599 Provider Contract Drift Checks MVP for External Schemas and Fields
  Scope: Focused provider contract drift checks for external schemas or field-shape changes.

Existing related work kept as linked tracks:

• Pandera Schema Drift Checks for Selected Pipelines #2594 Pandera Schema Drift Checks for Selected Pipelines
• Gold Schema Compatibility CI Gate (ADR-036 MVP) #2516 Gold Schema Compatibility CI Gate (ADR-036 MVP)

Parent roadmap remains #2511.