#Mocks

Mocks are the simplest way to customize scalar types (such as String or Int) and type fields (such as Book.title).

To customize scalar types, specify a function for each type:

const mocks = {
  String: () => 'my custom string',
  Int: () => faker.datatype.number({min: -500, max: 500}),
}

Poser already mocks a few scalar types:

import { faker } from '@faker-js/faker';

import type { Mocks } from '../types';

const defaultMocks: Mocks = {
  DateTime: () => faker.date.past().toISOString(),
  Int: () => faker.datatype.number(),
  JSON: () => faker.datatype.json(),
  String: () => faker.random.words(4),
};
export default defaultMocks;

You can overwrite these defaults by specifying your own, but they will only have effect in the service they live in.

Every field of every type (including Query and Mutation) can have a specific mock to return something else than the scalar type mock.

To customize type fields, specify a function for each field:

const mocks = {
  Book: {
    id: () => faker.datatype.uuid(),
    title: () => 'A fixed title for all books',
  }
}

This can also be done for Query fields, mostly to modify the default list length of 2:

import { utils } from '@datacamp/poser';

const mocks = {
  Query: {
    books: () => utils.mockList(20)
  }
}

In some cases, some fields depend on others, so mocking them one by one in isolation won't produce a result realistic enough.

For example, let's assume a type Task with the following fields:

type Task {
  progress: Float # Progress from 0 (not started) to 1 (completed)
  completedAt: Date
}

If these 2 fields must be coherent, we can't have a date in completedAt unless progress is set to 1.

This can be solved by using the __constructor function:

const mocks = {
  Task: {
    __constructor: (values: any = {}) => {
      // 20% chance a Task is completed
      const isCompleted = faker.datatype.number(100) < 20; 

      return {
        progress: isCompleted ? 1 : faker.datatype.float({min:0.1, max:0.9}),
        completedAt: isCompleted ? faker.date.recent() : null,
        ...values
      }
    },
    otherField: () => 'can still be mocked'
  }
}

The __constructor function will be called everytime a new instance is created, including store.insert(). When calling store.insert(), the second parameter contains values and is passed as the first parameter of __constructor. These values should be included in the return value of __constructor as shown above.