πŸ’‘ This page contain affiliate links. By making a purchase through them, we earn a commission at no extra cost to you.

How to Fix "serializes to the same string" Errors in Jest

Ferenc Almasi β€’ 2022 November 08 β€’ πŸ“– 1 min read
  • twitter
  • facebook

The "serializes to the same string" error happens in Jest when you try to expect an object to match a certain value, but you are using the wrong matcher. For example, you might have one of the following in your test case:

// ❌ Both of these examples will throw "erializes to the same string"
// Usin an array
expect([]).toBe([])

// Using an object
expect({}).toBe({})
Test throwing "serializes to the same string" error
Copied to clipboard!

In its simplest form (using an empty array or object), this test won't pass. This happens because each object reference is different in JavaScript. There are several ways to get around this. Use one of the following matchers in order to fix the error.

// βœ”οΈ This will work
const expected = []
const actual = []

// Using other matchers
expect(actual).toStrictEqual(expected)
expect(actual).toMatchObject(expected)

// Converting to a string
expect(JSON.stringify(actual)).toEqual(JSON.stringify(expected))
Using correct matchers for checking object equality
Copied to clipboard!
  • twitter
  • facebook
Did you find this page helpful?
πŸ“š More Webtips
Frontend Course Dashboard
Master the Art of Frontend
  • check Unlimited access to hundred of tutorials
  • check Access to exclusive interactive lessons
  • check Remove ads to learn without distractions
Become a Pro

Recommended