`expectTypeOf(A).toEqualTypeOf<B>()` does not cause Vitest to fail tests

[Dan503]

I have this basic getKeys function:

/** Strongly typed version of `Object.keys(object)` */
export function getKeys<ObjectType extends Record<string, any>>(object: ObjectType | undefined | null) {
  return Object.keys(object || {}) as Array<keyof ObjectType>;
}

And I have written these tests:

describe("getKeys", () => {
  it("should return an array of correctly typed keys", () => {
    const keysFromGetKeys = getKeys({ a: 1, b: "2" });
    const keysFromObjectKeys = Object.keys({ a: 1, b: "2" });

    expect(keysFromGetKeys).toEqual(["a", "b"]);
    expect(keysFromObjectKeys).toEqual(["a", "b"]);

    // These should cause the test to fail
    expectTypeOf(keysFromGetKeys).toEqualTypeOf<Array<string>>();
    expectTypeOf(keysFromObjectKeys).toEqualTypeOf<Array<"a" | "b">>();

    // these should pass
    expectTypeOf(keysFromGetKeys).toEqualTypeOf<Array<"a" | "b">>();
    expectTypeOf(keysFromObjectKeys).toEqualTypeOf<Array<string>>();
  });
});

However the vitest tests are still passing

I did add the --typecheck parameter to the npm "test": "vitest --typecheck" script.

I am using vitest for testing. Vitest is using expect-type for type testing.

I have installed the latest version of expect-type to ensure it isn't an issue of vitest using an outdated version.

I'm not sure if this is a bug in Vitest or a bug in expect-type.

Bug created against Vitest here:
vitest-dev/vitest#7691

[mmkal]

This is a vitest configuration problem, not a bug here.

Having said that, it comes up every now and then, so I'll keep it open so I don't forget - it may make sense to push a change that throws on usage of expectTypeOf outside of typechecked files.

Alternatively, once typescript-go is widely adopted, vitest might want to typecheck every test file by default since performance concerns will be mitigated.