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JavaScript Testing

Jest​

Jest is one of the most popular testing library for JavaScript (https://jestjs.io/). It works with projects using TypeScript. Jest is not fully supported by Vite but it is good to know some basics of Jest. For example, if we have a simple function:

function multiply(x, y) {
  return x * y;
}

Test case for the multiply function looks like the following:

test("test 2 * 3", () => {
  expect(multiply(2, 3)).toBe(6);
});
  • test function takes two arguments: a unique name and a test case. You can also use the alias it.
  • expect function is used when you want to test some values. It is normally used with matchers.
  • toBe is a Jest matcher that checks the value that function returns.

Depending on the value being tested, you should choose the correct matcher. More details about matchers can be found in the Jest documentation: https://jestjs.io/docs/using-matchers.

You can use the describe to group together related test cases.

describe("App component tests", () => {
  test("component renders", () => {
    // 1st test case
  });

  test("header text is shown", () => {
    // 2nd test case
  });
});

Further reading​