How to subvert typings of external-facing class constructor to test validation code

Question

I have an external/outward facing class. It contains input-validation code for instances where the library is imported into a JS environment (read: an environment that does not support type checking).

I am attempting to write unit tests specific to that validation code.

// function-token.ts;

// ...

export default class FunctionToken extends Token {
  constructor(token: IFunctionToken) {
    if (token == null) {
      throw new Error('token must be specified');
    }
    
    // ...

  }
}

Currently when I attempt to write a jestjs test for the validation code, the check fails due to typings:

// function-token.spec.ts

import FunctionToken from 'function-token';

test('throws an error when token is nullish', function () {
  // Expected 1 arguments, but got 0 - An argument for 'token' was not provided
  expect(() => new FunctionToken()).toThrow();

  // Argument of [undefined|null] is not assignable to IFunctionToken
  expect(() => new FunctionToken(undefined)).toThrow();
  expect(() => new FunctionToken(null)).toThrow();
});

How do I go about writing a test to subvert the type check with jestjs + ts-jest?

Note: Changing the underlying class's typing does not make sense as the validation is specific to cases where there is no type checking or enforcement.

Answer 1

Not sure how you'll get the parameterless call, but I think this is redundant because it defaults to undefined anyway. By casting the arguments to any you can bypass the parameter typings.

expect(() => new FunctionToken(undefined as any)).toThrow();
expect(() => new FunctionToken(null as any)).toThrow();

Alternativly you could just add // @ts-nocheck in testfiles concerning guard clauses.