How to create fake object from a data type in Typescript for testing

Question

I'm looking for a way to simplify making fake data for unit testing in Angular solution. I am using interfaces like:

export interface ReferenceDataItemCommon {
  codeDescription?: string;
  code: string;
  deleted?: boolean;
}

As data types in application. Currently using Factory.ts + Faker to create fake objects for purpose of tests:

  export const fakeReferenceDataItemCommon = Factory.Sync.makeFactory<ReferenceDataItemCommon>({
    code: Factory.each(() => Faker.lorem.word()),
    codeDescription: Factory.each(() => Faker.lorem.sentence(4)),
  });

But I'm curious if there is a way to simplify it even more for when you just want a object for your test and speed up creating it even more. Is it possible in Typescript to have a generic method that would return a object of that datatype?

  const fake = createFake<ReferenceDataItemCommon>();

What my initial idea was is to do something like:

Object.keys(object).forEach(key => {
  switch(typeof object[key]) {
    case 'string':
       object[key] = Faker.lorem.word();
       break;
  }
}
return object;

And for complex object call this method recursively. Is that possible, and if what would be a better approach to do this as I feel a bit out of my depth?

You cannot create values from types. TypeScript type information does not exist at run time. — Aluan Haddad
– Aluan Haddad, Commented Aug 15, 2020 at 12:10
I think this should be possible using code-generation. Where you'd create the factories with a cli, not at runtime. I'm currently looking for such a thing, might build it. — xiphe
– xiphe, Commented Apr 14, 2021 at 8:59

xiphe · Accepted Answer · 2021-04-14 09:08:01Z

3

When you create the factories with a cli, not at runtime it's possible:

https://www.npmjs.com/package/intermock looks promising

answered Apr 14, 2021 at 9:08

xiphe

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Comments

Gustavo Lopes · Accepted Answer · 2022-02-07 01:25:47Z

0

I was searching for something similar too but also didn't find it. So, I create this lib https://www.npmjs.com/package/class-validator-mocker, which works with classes annotated with class-validator decorators. If you can work with data classes instead of interfaces to define certain types, I think it's worth taking a look at it.

answered Feb 7, 2022 at 1:25

Gustavo Lopes

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