migrate-to-shoehorn

Migrate to Shoehorn

Why shoehorn?

shoehorn 允许你在 tests 中传入 partial data，同时保持 TypeScript 满意。它用 type-safe alternatives 替换 as assertions。

只用于 test code。 永远不要在 production code 中使用 shoehorn。

Tests 中 as 的问题：

• 会训练人忽略类型安全
• 必须手动指定 target type
• 对故意错误的数据需要 double-as（as unknown as Type）

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()	传入仍能 type-check 的 partial data
fromAny()	传入故意错误的数据（保留 autocomplete）
fromExact()	强制 full object（之后可换成 fromPartial）

Workflow

1. Gather requirements — 询问用户：

   • 哪些 test files 中的 as assertions 造成问题？
   • 是否在处理大型 objects，但只关心部分 properties？
   • 是否需要传入故意错误的数据来测试 error paths？

2. Install and migrate：

   • Install: npm i @total-typescript/shoehorn
   • 查找 test files 中的 as assertions: grep -r " as [A-Z]" --include="*.test.ts" --include="*.spec.ts"
   • 用 fromPartial() 替换 as Type
   • 用 fromAny() 替换 as unknown as Type
   • 添加来自 @total-typescript/shoehorn 的 imports
   • 运行 type check 验证