---
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
```bash
npm i @total-typescript/shoehorn
```
## Migration patterns
### Large objects with few needed properties
Before:
```ts
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:
```ts
import { fromPartial } from "@total-typescript/shoehorn";
it("gets user by id", () => {
getUser(
fromPartial({
body: { id: "123" },
}),
);
});
```
### `as Type` → `fromPartial()`
Before:
```ts
getUser({ body: { id: "123" } } as Request);
```
After:
```ts
import { fromPartial } from "@total-typescript/shoehorn";
getUser(fromPartial({ body: { id: "123" } }));
```
### `as unknown as Type` → `fromAny()`
Before:
```ts
getUser({ body: { id: 123 } } as unknown as Request); // wrong type on purpose
```
After:
```ts
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