AssertionError [ERR_ASSERTION] === BUG ???

Hello, I have solved the problem well but the test does not pass.

I have the error: assert.js:118 throw new AssertionError(obj); ^ AssertionError [ERR_ASSERTION]: Values have same structure but are not reference-equal: [ 1, 3, 1, 3 ] at /opt/project/test.ts:18:8

After a while I finally decided to copy exactly the same code as in the hints provided, and it returns the same error. I don't understand where the problem comes from. If someone could enlighten me it would be nice.

Here My code function isUnique(arr, el) { return arr.filter(a => a === el).length === 1 }

function nonUniqueElements(data: number[]): number[] { // your code here return data.filter(item => !isUnique(data, item)) }