TDD in action

There are some edge cases that we are not covering in our utils module. For example, what happens if we pass a string to the sum function?

import { sum } from "../utils.js";
const result = sum("1", 2); // 12

This is not the expected behavior when we use the sum function, so we need to fix it.

Let’s add some tests to cover these edge cases in our jest-tests/utils.test.js file:

describe("Utils Test Suite: sum", () => {
  it("Should sum two numbers", () => {
    expect(sum(1, 2)).toBe(3);
  });
  it("Should throw an error if we don't provide a valid number", () => {
    expect(() => sum("1", 2)).toThrow("Please provide a valid number");
  });
});

As you can see, we are using the toThrow matcher to test that the function is throwing an error. Now, let’s run the test coverage with npm...