JEST : Expect() only unique elements in an array - mongodb

Question

I am writing a test case using jest in to test the data returned from a method.The method returns array of non repeating elements.Now i am trying to use expect() in jest to test whether the array returned from the method has only unique elements.
Returned array from method
arr = [ 'Pizza' ,'Burger' , 'HotDogs'] // All elements are unique
Are there any jest matchers like below to check non repeating elements in array ?
expect(arr).toBeUnique()
Or any logic using existing matchers should be done ?

Answer 1

There is no built on the method to check that array has a unique value, but I would suggest doing something like that:
const goods = [ 'Pizza' ,'Burger' , 'HotDogs'];
const isArrayUnique = arr => Array.isArray(arr) && new Set(arr).size === arr.length; // add function to check that array is unique.
expect(isArrayUnique(goods)).toBeTruthy();
You can use expect.extend to add your own matchers to Jest.
For example:
expect.extend({
toBeDistinct(received) {
const pass = Array.isArray(received) && new Set(received).size === received.length;
if (pass) {
return {
message: () => `expected [${received}] array is unique`,
pass: true,
};
} else {
return {
message: () => `expected [${received}] array is not to unique`,
pass: false,
};
}
},
});
and use it:
const goods = [ 'Pizza' ,'Burger' , 'HotDogs'];
const randomArr = [ 'Pizza' ,'Burger' , 'Pizza'];
expect(goods).toBeDistinct(); // Passed
expect(randomArr).toBeDistinct(); // Failed

Answer 2

This is very similar to Yevhen's answer but I've changed the error message to describe the first duplicate item encountered, like
item 3 is repeated in [1,2,3,3]
at the expense of sorting the array
expect.extend({
toContainUniqueItems(received) {
const items = [...(received || [])];
items.sort();
for (let i = 0; i < items.length - 1; i++) {
if (items[i] === items[i + 1]) {
return {
pass: false,
message: () => `item ${items[i]} is repeated in [${items}]`,
};
}
}
return {
pass: true,
message: () => `all items are unique in [${items}]`,
};
},
});