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2704. To Be Or Not To Be

DifficultyEasy

Description

Write a function expect that helps developers test their code. It should take in any value val and return an object with the following two functions.

  • toBe(val) accepts another value and returns true if the two values === each other. If they are not equal, it should throw an error "Not Equal".
  • notToBe(val) accepts another value and returns true if the two values !== each other. If they are equal, it should throw an error "Equal".

 

Example 1:

Input: func = () => expect(5).toBe(5)
Output: {"value": true}
Explanation: 5 === 5 so this expression returns true.

Example 2:

Input: func = () => expect(5).toBe(null)
Output: {"error": "Not Equal"}
Explanation: 5 !== null so this expression throw the error "Not Equal".

Example 3:

Input: func = () => expect(5).notToBe(null)
Output: {"value": true}
Explanation: 5 !== null so this expression returns true.

Solutions

Solution 1

Thinking

The assertion object must throw the prescribed errors on the equal and unequal paths and return \(true\) on success. Two free-standing helpers would duplicate the comparison.

A closure keeps the expected value \(val\) and returns \(\{toBe, notToBe\}\): the former throws Not Equal on \(!==\), the latter throws Equal on \(===\). All state needed for chaining lives in that closure.

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type ToBeOrNotToBe = {
    toBe: (val: any) => boolean;
    notToBe: (val: any) => boolean;
};

function expect(val: any): ToBeOrNotToBe {
    return {
        toBe: (toBeVal: any) => {
            if (val !== toBeVal) {
                throw new Error('Not Equal');
            }
            return true;
        },
        notToBe: (notToBeVal: any) => {
            if (val === notToBeVal) {
                throw new Error('Equal');
            }
            return true;
        },
    };
}

/**
 * expect(5).toBe(5); // true
 * expect(5).notToBe(5); // throws "Equal"
 */

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/**
 * @param {string} val
 * @return {Object}
 */
var expect = function (val) {
    return {
        toBe: function (expected) {
            if (val !== expected) {
                throw new Error('Not Equal');
            }
            return true;
        },
        notToBe: function (expected) {
            if (val === expected) {
                throw new Error('Equal');
            }
            return true;
        },
    };
};

/**
 * expect(5).toBe(5); // true
 * expect(5).notToBe(5); // throws "Equal"
 */

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