How to add custom message to Jest expect?

Question

Image following test case:

it(\'valid emails checks\', () => {
  [\'abc@y.com\', \'a@b.nz\'/*, ...*/].map(mail => {
    expect(isValid(mail)).toBe(true);
          


        

Answer 1

You can rewrite the expect assertion to use toThrow() or not.toThrow(). Then throw an Error with your custom text. jest will include the custom text in the output.

// Closure which returns function which may throw
function isValid (email) {
  return () => {
     // replace with a real test!
     if (email !== 'some@example.com') {
       throw new Error(`Email ${email} not valid`)
     }
  }
}

expect(isValid(email)).not.toThrow()