use internals DI seam pattern for test-injectable functions

Trigger

• (no explicit trigger metadata; cluster derived from category/tags)

Required Procedure

• use _internals DI seam pattern for test-injectable functions
• spread real module exports when mocking node built-ins (import * as real from 'node:module'; mock.module('node:module', () => ({ ...real, targetFn: mockFn })))
• verify mock isolation by running test files in combined mode, not individually

Forbidden Shortcuts

• rely on mock.module() isolation between test files in bun:test
• declare a test passing based solely on individual file execution

Delegation Template

When delegating a task affected by this skill, include:

SKILLS: file:.opencode/skills/generated/use-internals-di-seam-pattern-for-test-injectable-functions/SKILL.md

Reviewer Checks

• Verify each required action above appears in the diff.

Test Engineer Checks

• Add or update tests covering the trigger condition and the forbidden shortcut.

Source Knowledge IDs

• 8a374ec6-734e-4b34-9119-1b6148db3a1e — In Bun's shared test-runner process, mock.module() leaks across test files. Always use _internals DI seams or spread-real-exports for node:fs/child_process mocks instead of bare mock.module().