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migrate-to-shoehorn

Skill8 starsChanged 2 months agoMITView on GitHub

Migrate unsafe TypeScript test assertions to @total-typescript/shoehorn with explicit fixture intent. Use when test files contain unsafe `as` or `as unknown as` typecasts, when mock fixtures break under typechecking, or when modernizing test typing — even if the user says \"fix test type assertions\". Do NOT use for production code types.

  • Installs packages

We split this skill into the rules it gives an agent

4 rules. 0 are common, 2 are distinctive, and 2 are very specific to this project.

  • 0

    Common

    Most of the 75 edited versions we read keep these.

  • 2

    Distinctive

    This author's own choices. Worth a look.

  • 2

    Very specific

    Tied to their project's names, files or tools. Probably skip.

  • Common
  • Distinctive
  • Very specific
  1. Very specific:

    Mandatory Typecheck Green: Every migration pass must conclude with a green tsc --noEmit or equivalent repository typecheck command.

    line 21
  2. Very specific:

    Key Point: Check that it is added strictly to devDependencies.

    line 43
  3. Distinctive:

    Action: Search test files for type assertion smells:

    line 47
  4. Distinctive:

    Key Point: Verify that tests pass and TypeScript emits 0 errors.

    line 63

“Common” is measured: kept by at least 6 in 10 of the 75 edited versions of this file we could read. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.

Keep what fits and drop the rest. Your version, ready for your agents.
Files
SKILL.md

Migrate to Shoehorn

Safely migrate unsafe, brittle TypeScript test-fixture typecasts (as Type, as unknown as Type) to intention-revealing, type-safe helpers from @total-typescript/shoehorn.

Core Invariants

  1. Test-Code Isolation Strictly: @total-typescript/shoehorn is strictly for test suites and test fixtures; NEVER import or use shoehorn helpers in production application code.
  2. Intent-Specific Helper Mapping:
    • Partial objects where only some keys matter $\rightarrow$ fromPartial(obj)
    • Intentionally invalid/wrong types for error testing $\rightarrow$ fromAny(obj)
    • Fully populated mocks $\rightarrow$ fromExact(obj)
  3. Preserve Autocomplete & Refactor Safety: Maintain TypeScript type inference and IDE autocompletion across all migrated test fixtures.
  4. Automated Discovery & Regex Caution: Discover test casts via targeted grep (as [A-Z]); avoid blind global replacements that might alter production code.
  5. Mandatory Typecheck Green: Every migration pass must conclude with a green tsc --noEmit or equivalent repository typecheck command.

Architecture & Map of Content (MOC)

[ Unsafe Test Casts (`as Type`, `as unknown as`) ] ──► [ Intent Classification ] ──► [ Replace with Shoehorn Helper ] ──► [ Verify Typecheck ]
Unsafe PatternShoehorn ReplacementTarget Scenario
{ id: "123" } as UserfromPartial<User>({ id: "123" })Test cares only about id in large type
{ id: 123 } as unknown as UserfromAny<User>({ id: 123 })Testing runtime validation on bad input
completeMock as UserfromExact<User>(completeMock)Explicit complete mock structure

Step-by-Step Procedure (TWI)

Step 1: Install Dependency with Detected Package Manager

  • Action: Install @total-typescript/shoehorn as a devDependency (bun add -d, pnpm add -D, npm i -D).
  • Key Point: Check that it is added strictly to devDependencies.
  • Why: Prevent bundling test-helper utilities into production builds.

Step 2: Locate Unsafe Casts in Test Files

  • Action: Search test files for type assertion smells:
    grep -rnE " as [A-Z]| as unknown as " --include="*.test.ts" --include="*.spec.ts" src/
  • Key Point: Inspect surrounding context to determine whether the fixture is a partial mock or an intentionally invalid payload.
  • Inline Checklist:
    • Only test files (*.test.ts, *.spec.ts) targeted
    • Zero production source files modified
    • Intent classified per fixture (fromPartial vs. fromAny)

Step 3: Replace Casts and Import Helpers

  • Action: Replace as Type with fromPartial(...) and as unknown as Type with fromAny(...), adding import { fromPartial, fromAny } from "@total-typescript/shoehorn".
  • Why: fromPartial documents that missing fields are deliberate, avoiding false compiler errors while retaining type intelligence.

Step 4: Run Typecheck & Test Suite

  • Action: Execute the project's typecheck command (e.g. bun run typecheck, pnpm check, tsc --noEmit) and run the test suite.
  • Key Point: Verify that tests pass and TypeScript emits 0 errors.
  • Why: Ensures no subtle type contract regressions were introduced during migration.

Anti-Rationalization Guardrails

Tempting RationalizationBinding RuleEngineering Rationale
"Use shoehorn in production helpers to bypass strict types."Forbidden. Test code only.Bypassing types in production creates silent runtime TypeError crashes.
"Use fromAny everywhere because it's easier than fromPartial."Use fromPartial for valid partials; fromAny only for invalid types.Overusing fromAny disables autocomplete and typechecking benefits.
"Skip running typecheck after updating test files."Mandatory green typecheck verification.Minor syntax errors or missing generic arguments break CI builds.

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