/migrate-to-shoehorn

name: migrate-to-shoehorn
description: 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.

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

| Function | Use 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