SKILL.md
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/shoehornMigration 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 purposeAfter:
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
-
Gather requirements - ask user:
- What test files have
asassertions causing problems?
- Are they dealing with large objects where only some properties matter?
- Do they need to pass intentionally wrong data for error testing?
-
Install and migrate:
- Install:
npm i @total-typescript/shoehorn
- Find test files with
asassertions:grep -r " as [A-Z]" --include="*.test.ts" --include="*.spec.ts"
- Replace
as TypewithfromPartial()
- Replace
as unknown as TypewithfromAny()
- Add imports from
@total-typescript/shoehorn
- Run type check to verify