charlieigg/fishery

A library for setting up JavaScript objects as test data

Fishery

Fishery is a library for setting up JavaScript objects for use in tests, Storybook, and anywhere else you need to set up data. It is loosely modeled after the Ruby gem, factory_bot.

Fishery is built with TypeScript in mind. Factories accept typed parameters and return typed objects, so you can be confident that the data used in your tests is valid. If you aren't using TypeScript, that's fine too – Fishery still works, just without the extra typechecking that comes with TypeScript.

Installation

Install fishery with:

npm install --save fishery

or

yarn add fishery

Usage

A factory is just a function that returns your object. Fishery provides several arguments to your factory function to help with common situations. After defining your factory, you can then call build() on it to build your objects. Here's how it's done:

Define factories

// factories/user.ts
import { Factory } from 'fishery';
import { User } from '../my-types';

export default Factory.define<User>(({ sequence, factories }) => ({
  id: sequence,
  name: 'Bob',
  address: { city: 'Grand Rapids', state: 'MI', country: 'USA' },
  posts: factories.post.buildList(2),
}));

Combine factories

Now combine your factories together and register them:

// factories/index.ts
import { register } from 'fishery';
import user from './user';
import post from './post';

export const factories = register({
  user,
  post,
});

Build objects with your factories

Pass parameters as the first argument to build to override your factory defaults. These parameters are deep-merged into the default object returned by your factory.

build also supports a seconds argument with the following keys:

• transient: data for use in your factory that doesn't get overlaid onto your result object. More on this in the Transient Params section
• associations: often not required but can be useful in the case of bi-directional associations. More on this in the Associations section

// my-test.test.ts
import { factories } from './factories';

const user = factories.user.build({
  name: 'Susan',
  address: { city: 'Detroit' },
});

user.name; // Susan
user.address.city; // Detroit
user.address.state; // MI (from factory)

Documentation

Typechecking

Factories are fully typed, both when defining your factories and when using them to build objects, so you can be confident the data you are working with is correct.

const user = factories.user.build();
user.foo; // type error! Property 'foo' does not exist on type 'User'

const user = factories.user.build({ foo: 'bar' }); // type error! Argument of type '{ foo: string; }' is not assignable to parameter of type 'Partial<User>'.

export default Factory.define<User, Factories, UserTransientParams>(
  ({ sequence, params, transientParams, associations, afterCreate }) => {
    params.firstName; // Property 'firstName' does not exist on type 'DeepPartial<User>
    transientParams.foo; // Property 'foo' does not exist on type 'Partial<UserTransientParams>'
    associations.bar; // Property 'bar' does not exist on type 'Partial<User>'

    afterCreate(user => {
      user.foo; // Property 'foo' does not exist on type 'User'
    });

    return {
      id: `user-${sequence}`,
      name: 'Bob',
      post: null,
    };
  },
);

Associations

If your factory references another factory, use the factories object provided to the factory:

const postFactory = Factory.define<Post, Factories>(({ factories }) => ({
  title: 'My Blog Post',
  author: factories.user.build(),
}));

If you'd like to be able to pass in an association when building your object and short-circuit the call to factories.xxx.build(), use the associations variable provided to your factory:

const postFactory = Factory.define<Post, Factories>(
  ({ factories, associations }) => ({
    title: 'My Blog Post',
    author: associations.author || factories.user.build(),
  }),
);

Then build your object like this:

factories.post.build({}, { associations: { author: susan } });

Typing the factories factory argument

In the above examples, the Factories generic parameter is passed to define. This is optional but recommended in order to get type-checking of the factories object. You can define your Factories type like this:

// factories/types.ts
export interface Factories {
  user: Factory<User>;
  post: Factory<Post>;
}

Once you've defined your Factories type, it can also be used when registering your factories. This ensures that your Factories type is always in sync with the actual factories that you have registered:

// factories/index.ts
import { register } from 'fishery';
import user from './user';
import post from './post';
import { Factories } from './types';

export const factories: Factories = register({ user, post });

Use params to access passed in properties

The parameters passed in to build are automatically overlaid on top of the default properties defined by your factory, so it is often not necessary to explicitly access the params in your factory. This can, however, be useful, for example, if your factory uses the params to compute other properties:

const userFactory = Factory.define<User, Factories>(({ params }) => {
  const { name = 'Bob Smith' } = params;
  const email = params.email || `${kebabCase(name)}@example.com`;

  return {
    name,
    email,
    posts: [],
  };
});

Params that don't map to the result object (transient params)

Factories can accept parameters that are not part of the resulting object. We call these transient params. When building an object, pass any transient params in the second argument:

const user = factories.user.build({}, { transient: { registered: true } });

Transient params are passed in to your factory and can then be used however you like:

interface User {
  name: string;
  posts: Post[];
  memberId: string | null;
  permissions: { canPost: boolean };
}

interface UserTransientParams {
  registered: boolean;
  numPosts: number;
}

const userFactory = Factory.define<User, Factories, UserTransientParams>(
  ({ transientParams, factories, sequence }) => {
    const { registered, numPosts = 1 } = transientParams;

    const user = {
      name: 'Susan Velasquez',
      posts: factories.posts.buildList(numPosts),
      memberId: registered ? `member-${sequence}` : null,
      permissions: {
        canPost: registered,
      },
    };
  },
);

In the example above, we also created a type called UserTransientParams and passed it as the third generic type to define. This isn't required but gives you type checking of transient params, both in the factory and when calling build.

When constructing objects, any regular params you pass to build take precedence over the transient params:

const user = factories.user.build(
  { memberId: '1' },
  { transient: { registered: true } },
);
user.memberId; // '1'
user.permissions.canPost; // true

After-create hook

You can instruct factories to execute some code after an object is created. This can be useful if a reference to the object is needed, like when setting up relationships:

export default Factory.define<User, Factories>(
  ({ factories, sequence, afterCreate }) => {
    afterCreate(user => {
      const post = factories.post.build({}, { associations: { author: user } });
      user.posts.push(post);
    });

    return {
      id: sequence,
      name: 'Bob',
      posts: [],
    };
  },
);

Defining one-off factories without calling register

Factories should usually be defined and then combined together using register:

// factories/index.ts
import { register } from 'fishery';
import user from './user';
import post from './post';
import { Factories } from './types';

export const factories: Factories = register({ user, post });

The factories passed to register get injected into each factory so factories can access each other. This prevents circular dependencies that could arise if your factories try to access other factories directly by importing them and also creates a convenient way for factories to access other factories without having to explicitly import them.

If you are defining a factory for use in a single test file, you might not wish to register the factory or use the factories object that gets injected to the factory. In this case, you can use defineUnregistered instead of define and then skip calling register, eg:

const personFactory = Factory.defineUnregistered<Person>(() => ({
  name: 'Sasha',
}));

const person = personFactory.build();

Contributing

See the CONTRIBUTING document. Thank you, contributors!

Credits

This project name was inspired by Patrick Rothfuss' Kingkiller Chronicles books. In the books, the artificery, or workshop, is called the Fishery for short. The Fishery is where things are built.

License

Fishery is Copyright © 2020 Stephen Hanson and thoughtbot. It is free software, and may be redistributed under the terms specified in the LICENSE file.

About thoughtbot

Fishery is maintained and funded by thoughtbot, inc. The names and logos for thoughtbot are trademarks of thoughtbot, inc.

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