migrate to shoehorn

Skill

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.

Files1
  • @skills/migrate-to-shoehorn/SKILL.md

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

bash
npm i @total-typescript/shoehorn

Migration patterns

Large objects with few needed properties

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

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

as Type → fromPartial()

Before:
typescript
getUser({ body: { id: "123" } } as Request);
After:
typescript
import { fromPartial } from "@total-typescript/shoehorn";

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

as unknown as Type → fromAny()

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