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a skill by mattpocock, brought here by kt

migrate to shoehorn

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/skills/mattpocock-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.

kindskill
last tended2026-10-12
written bymattpocock
sourcegithub.com/mattpocock/skills
kept currentwith its source · last read 2026-10-12
in the foldermattpocock skills · 15 of 36 · ‹ loop me · pr ›
brought here bykt
reuseMIT
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reading2 min

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. 1Gather 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?
  1. 1Install 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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