Edit in JSFiddle

/**
 * Calculate the age in years of a person.
 *
 * @param {Person} p A Person object implementing a birth Date parameter.
 * @return {number} The age in years of p.
 */
function calculate_age(p) {
    let thisYear = new Date().getFullYear();
    let personYear = p.birth.getFullYear();
    let age = thisYear - personYear;
    return age;
}

var bertignac = {
    name: "Louis Bertignac",
    birth: new Date(1954, 01, 23)
}

QUnit.test("Standard usage", function(assert) {
    let thisYear = 63;
    assert.equal(calculate_age(bertignac), thisYear, "Correct age");  
    assert.equal(calculate_age({birth: new Date(1954, 01, 23)}), thisYear, "Correct age");  
});