How to unit test exception thrown in TypeScript class's constructor in JestJs

Question

I am building some application in NestJs, therefore the default unit test framework is JestJs. Assume I have following class My.ts

export My { constructor(private myValue: number) { if (myValue ==== null) { throw new Error('myValue is null'); } } }

I have created my unit test class My.spec.ts

import { My } from './My'; describe('My', () => { fit('Null my value throws', () => { expect(new My(null)).rejects.toThrowError('myValue is null'); }); });

I use the command npm run test to run the unit tests, instead of getting what I expected I had a failure to complain the code in my My class constructor that an exception is thrown.

What is the proper way to write unit test code in Jest to test the exception logic in constructor?

hardywang · Accepted Answer · 2019-01-15 21:07:26Z

After I did my research following codes work for me

import { My } from './My'; describe('My', () => { fit('Null my value throws', () => { expect(() => {new My(null);}).toThrow('myValue is null'); }); });

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