TSNode + Mocha: Ignore TypeScript errors (make compiler emit on errors and make TSNode execute emitted code) - node.js

Question

In the below code, although function test2 in invalid, it should not affect to testing of function test1:
export function test1(): boolean {
return true;
}
export function test2(): number {
return "1";
}
Test:
import { assert as Assert } from "chai";
import { test1 } from "./example";
describe("Example", (): void => {
it("Example", (): void => {
Assert.isTrue(test1());
});
});
However Mocha, executed by TSNode will fail:
TSError: ⨯ Unable to compile TypeScript:
Source/ProjectBuilder/example.ts(6,3): error TS2322: Type '"1"' is not assignable to type 'number'.
Possible to force TSNode to complete above test? TypeScript has option noEmitOnError...
My mocharc.yaml:
extension:
- ts
spec: "**/*.test.ts"
require:
- ts-node/register
- tsconfig-paths/register
Why I need it
According the Clean Architecture, "Business rules must not depends on anything, and it must be testable". But even if business rules does not depend on views, controllers, etc., we can not test it if some errors in views, controllers, etc. exists.
When I modify business logic in my application, all that depend on it becomes invalid. Assume that in my entity in business logic type User { name: string; age: number } has been changed to type User { fullName: string; age: string; }. All that depend on business logic (view, controllers, presenters, etc.) becomes invalid - I need to correct it too according updated to business logic.
// In business rules:
type User = {
ID: number;
fullName: string;
age: string; // in past - number
}
// In controller:
class UserProfileController {
// ...
// All what comes from input field is string ↓
private onClickChangeUserAge(inputtedUserAge: string) {
// This expression obeys to previous version of business rules!
this.targetUser.age = Number(inputtedUserAge);
// TypeScript will emit type error, when I try to test business rules,
// however business rules does not depend on controller.
}
}
However, in big application, this corrections could takes days, weeks and months. How we can get the feedback proves that at least business logic works properly and we are in right way?

Answer 1

It would not make sense for you to ask Typescript to disregard types. What you are describing is akin to asking for a calculator that confirms that 2 + 2 = 5, only temporarily, because eventually you will ask for 2 + 3 = 5 but that might take a very long time.
The assumption in your question is that number and string are sufficiently compatible that your business logic will be sound regardless of whether test2 returns 1 or "1". This is not true: By way of example, 1 + 1 == 2, "1" + 1 == "11", and "1" - 1 == 0. Depending on which of those applies to your case, disregarding types may allow you to test your business logic, or may give you false confidence in a broken system. I would venture that in general the data types count as part of the business logic you're trying to verify--what would the data model count as, if not business logic?
Instead, what you are describing is a gradual migration during which the business rules ensure that test2 returns string | number. By describing the migration accurately in the type system, you may be able to confirm that the business logic applies correctly--if that is true across your migration--and also provide a type that you can apply only from certain modules and call sites that can be tightened up as you finish the migration.

Answer 2

type User = {
ID: number;
fullName: string;
age: string | number
}
You can specify both types to make migration easier and not use //#ts-ignore everywhere.
This will add proper suggestions everywhere like: