chai assert interface

const assert= require("chai").assert; let aBook= { price: 10 }; function loweringPrice() { aBook.price-= 1; } function getThePrice() { return aBook.price; } // returning the object function getTheBook() { return aBook; } assert.decreasesBy(loweringPrice, aBook, 'price', 1); assert.decreases(loweringPrice, getThePrice, 'price'); // awkward fail assert.decreasesBy(loweringPrice, getThePrice, 'price', 1); assert.decreasesBy(loweringPrice, getTheBook, 'price', 1);