Listing 4. Suites usually include several test cases.

describe("Prime numbers tests", function() {
  it("Test prime numbers", function() {
    expect(isPrime(2)).to.be.true();
    expect(isPrime(5)).to.be.true();
  });

  it("Test non-prime numbers", function() {
    expect(isPrime(1).to.be.false();
    expect(isPrime(4).to.be.not.true(); // just for variety!
    expect(isPrime(NaN)).to.throw(err);
  });
});