==== tests/cases/compiler/derivedTypeIncompatibleSignatures.ts (2 errors) ====
    interface A {
        (a: string): string;
    }
    
    interface B extends A {
        (a: string): number; // Number is not a subtype of string.  Should error.
    }
    
    interface C {
        new (a: string): string;
    }
    
    interface D extends C {
        new (a: string): number; // Number is not a subtype of string.  Should error.
    }
    
    interface E {
        [a: string]: string;
    }
    
    interface F extends E {
              ~
!!! Interface 'F' incorrectly extends interface 'E':
!!!   Index signatures are incompatible:
!!!     Type 'number' is not assignable to type 'string'.
        [a: string]: number; // Number is not a subtype of string.  Should error.
    }
    
    interface G {
        [a: number]: string;
    }
    
    interface H extends G {
              ~
!!! Interface 'H' incorrectly extends interface 'G':
!!!   Index signatures are incompatible:
!!!     Type 'number' is not assignable to type 'string'.
        [a: number]: number; // Should error for the same reason
    }