Since #33860 we get false compile errors when spying on overloaded methods.

Minimal example:

interface I {
  f(): string;
  f(x: any): number;
}

const spyObject = jasmine.createSpyObj<I>("spyObject", ["f"]);
spyObject.f.and.returnValue("a string, erroneously required to be a number");

Results in:

TS2345: Argument of type '"a string, erroneously required to be a number"' is not assignable to parameter of type 'number'.

Our expectation: The accepted parameter type of returnValue should be string | number, not only number.

(Unfortunately the problematic method overloading (as demonstrated in the I example interface) occurs in external libraries we use, so we can't change that part.)

CC PR author: @kolodny