t.js

// Good 
describe("[unit of work]", () => {
  it("should [expected behaviour] when [scenario/context]", () => {});
});

// Better
describe("[unit of work]", () => {
  describe("when [scenario/context]", () => {
    it("should [expected behaviour]", () => {});
  });
});

// Best 
describe("The Gallery instance", () => {
  describe("when initialized", () => {
    it("should properly calculate the thumb size", () => {});
    it("should properly calculate the thumbs count", () => {});
  });
});