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Methodologygeneric

migrate-to-shoehorn

Migrate test files from `as` type assertions to @total-typescript/shoehorn. Use when user mentions shoehorn, wants to replace `as` in tests, or needs partial test data.

mattpocock/skills
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Install

npx skills add https://github.com/mattpocock/skills --skill migrate-to-shoehorn

Use with your agent

ClaudeCursorOpenAIGemini

Install the migrate-to-shoehorn skill, then use it as build context. Run: npx skills add https://github.com/mattpocock/skills --skill migrate-to-shoehorn. Then read the installed skill.md and follow its guidance to build or refactor my project.

Migrate to Shoehorn

Why shoehorn?

shoehorn lets you pass partial data in tests while keeping TypeScript happy. It replaces as assertions with type-safe alternatives.

Test code only. Never use shoehorn in production code.

Problems with as in tests:

  • Trained not to use it
  • Must manually specify target type
  • Double-as (as unknown as Type) for intentionally wrong data

Install

npm i @total-typescript/shoehorn

Migration patterns

Large objects with few needed properties

Before:

type Request = {
  body: { id: string };
  headers: Record<string, string>;
  cookies: Record<string, string>;
  // ...20 more properties
};

it("gets user by id", () => {
  // Only care about body.id but must fake entire Request
  getUser({
    body: { id: "123" },
    headers: {},
    cookies: {},
    // ...fake all 20 properties
  });
});

After:

import { fromPartial } from "@total-typescript/shoehorn";

it("gets user by id", () => {
  getUser(
    fromPartial({
      body: { id: "123" },
    }),
  );
});

as Type → fromPartial()

Before:

getUser({ body: { id: "123" } } as Request);

After:

import { fromPartial } from "@total-typescript/shoehorn";

getUser(fromPartial({ body: { id: "123" } }));

as unknown as Type → fromAny()

Before:

getUser({ body: { id: 123 } } as unknown as Request); // wrong type on purpose

After:

import { fromAny } from "@total-typescript/shoehorn";

getUser(fromAny({ body: { id: 123 } }));

When to use each

FunctionUse case
fromPartial()Pass partial data that still type-checks
fromAny()Pass intentionally wrong data (keeps autocomplete)
fromExact()Force full object (swap with fromPartial later)

Workflow

  1. Gather requirements - ask user:

    • What test files have as assertions causing problems?
    • Are they dealing with large objects where only some properties matter?
    • Do they need to pass intentionally wrong data for error testing?

  2. Install and migrate:

    • Install: npm i @total-typescript/shoehorn
    • Find test files with as assertions: grep -r " as [A-Z]" --include="*.test.ts" --include="*.spec.ts"
    • Replace as Type with fromPartial()
    • Replace as unknown as Type with fromAny()
    • Add imports from @total-typescript/shoehorn
    • Run type check to verify