migrate-to-shoehorn
把測試裡的 as 斷言換成 shoehorn
中文翻譯
---
name: migrate-to-shoehorn
description: 把測試檔從 `as` 型別斷言遷移到 @total-typescript/shoehorn。當使用者提到 shoehorn、想取代測試裡的 `as`，或需要部分的測試資料時使用。
---
# 遷移到 Shoehorn
## 為什麼用 shoehorn？
`shoehorn` 讓你在測試裡傳入部分資料，同時讓 TypeScript 滿意。它用型別安全的替代方案取代 `as` 斷言。
**只用在測試程式碼。** 絕對不要在 production 程式碼裡用 shoehorn。
測試裡用 `as` 的問題：
- 我們被訓練成不要用它
- 必須手動指定目標型別
- 故意傳錯誤資料時要用雙重 as（`as unknown as Type`）
## 安裝
```bash
npm i @total-typescript/shoehorn
```
## 遷移模式
### 大型物件，只需要少數屬性
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 } }));
```
## 各自什麼時候用
| 函式 | 使用情境 |
| --------------- | -------------------------------------------------- |
| `fromPartial()` | 傳入部分資料，而且仍然能通過型別檢查 |
| `fromAny()` | 傳入刻意錯誤的資料（保留自動完成） |
| `fromExact()` | 強制要完整物件（之後可以換成 fromPartial） |
## 工作流程
1. **收集需求** - 問使用者：
- 哪些測試檔有 `as` 斷言造成問題？
- 他們是不是在處理大型物件，而且只有部分屬性重要？
- 他們是不是需要為了測試錯誤情況而傳入刻意錯誤的資料？
2. **安裝並遷移**：
- [ ] 安裝：`npm i @total-typescript/shoehorn`
- [ ] 找出有 `as` 斷言的測試檔：`grep -r " as [A-Z]" --include="*.test.ts" --include="*.spec.ts"`
- [ ] 把 `as Type` 換成 `fromPartial()`
- [ ] 把 `as unknown as Type` 換成 `fromAny()`
- [ ] 從 `@total-typescript/shoehorn` 加上 import
- [ ] 跑型別檢查來驗證英文原文
---
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