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

Although it's not a general solution, for the common case of wanting a custom exception message to distinguish items in a loop, you can instead use Jest's test.each.

For example, your sample code:

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

Could instead become

test.each(
    ['abc@y.com', 'a@b.nz'/*, ...*/],
    'checks that email %s is valid',
    mail => {
        expect(isValid(mail)).toBe(true);
    }
);

Answer 2

You can use try-catch:

try {
    expect(methodThatReturnsBoolean(inputValue)).toBeTruthy();
}
catch (e) {
    throw new Error(`Something went wrong with value ${JSON.stringify(inputValue)}`, e);
}