==== tests/cases/compiler/numberToString.ts (2 errors) ====
    function f1(n:number):string {
        return n; // error return type mismatch
               ~
!!! Type 'number' is not assignable to type 'string'.
    }
    
    function f2(s:string):void {
    }
    
    f1(3);
    f2(3); // error no coercion to string
       ~
!!! Argument of type 'number' is not assignable to parameter of type 'string'.
    f2(3+""); // ok + operator promotes