Angular - Testing an @Input with a set attached to it

I have a component which takes an argument as a sort of directive to set the size of the <div> within its template, the only problem now is that I am unsure how to test it?

I call my component like this, where small can be replaced with other pre-defined sizes such as medium/large etc:

<spinner small></spinner>

I then take this as an @Input(<size>) and perform a set to change a size variable that is then passed into an [ngStyle] to change the CSS of the displayed component size.

component.ts

size: number;

@Input('small') set small(value) {
  this.size = !value ? 25 : this.size;
}

get getSize() {
  const myStyle = {
    width: this.size + 'px',
    height: this.size + 'px'
  };
  return myStyle;
}

component.html

<div [ngStyle]="getSize"></div>

I have successfully tested the get getSize() function, but I have become a bit stuck around the @Input(<val>) set functions :-/