==== tests/cases/compiler/optionalPropertiesInClasses.ts (1 errors) ====
    interface ifoo {
        x?:number;
        y:number;
    }
    
    class C1 implements ifoo {
        public y:number;
    }
    
    class C2 implements ifoo { // ERROR - still need 'y'
          ~~
!!! optionalPropertiesInClasses.ts(10,7): error TS2137: Class C2 declares interface ifoo but does not implement it:
!!! 	Type 'C2' is missing property 'y' from type 'ifoo'.
        public x:number;
    }
    
    class C3 implements ifoo {
        public x:number;
        public y:number;
    }