Zaha

Zaha is a javascript utility for generating test builders! Builders allow you to:

1. Quickly create test objects automatically populated with default fields
2. Abstract the structure of complex objects behind a fluent interface

Get Started

First, you'll want to install the library:

npm i -D zaha

Then create a test builder:

// room-builder.js
 
import zaha, { is } from 'zaha';
 
export default zaha({
  length: is.number(),
  width: is.number(),
  furniture: is.arrayOf(is.string())
});

Then use your new builder in a test!

// room.spec.js
 
import RoomBuilder from './room-builder';
 
const room = new RoomBuilder()
  .withWidth(500),
  .withFurniture(['chair', 'bed'])
  .build();

Details

Zaha is a function which takes as input a schema and outputs a builder class.

Schemas

A schema is an object whose fields are all builders. It defines what fields you want your eventually build object to contain. The following example of a schema defines an object with a string and numeric field, for instance.

import { is } from 'zaha';
 
const schema = {
  name: is.string(),
  age: is.number()
};

is

You might notice that this mystical is object can be used to define the types of fields. is provides the following:

• is(value): An exact value the field should be when the final object is built
• is.string(): A string field
• is.datestring(): A string which represents a date
• is.number(): A decimal number
• is.int(): An integer number
• is.boolean(): A boolean value
• is.object(schema): Converts the schema into a basic builder; useful for nested structures
• is.array(): Defines an array of any type
• is.arrayOf(builder): Defines an array of the provided builder type
• is.function(): A callable function
• is.oneOf(values): Value must be exactly one of the provided values; values is an array

The following example shows how to use is.object and is.arrayOf:

const schema = {
  nested: is.object({
    array: is.arrayOf(is.int()),
    exact: is('This particular string')
  })
};

Zaha Builders

Though is is useful, in reality these fields can take any builder. A builder object is simply an object which has the build() method defined on it. This means you can pass in builders created by Zaha into the schema:

const InnerBuilder = zaha(innerSchema);
 
const schema = {
  value: new InnerBuilder()
};

Custom Builders

A builder is any object which has build() defined on it. This means you can make your own collection of domain-specific basic builders that you can pass to a Zaha schema.

const randomString = {
  build: () => random.string()
};
 
const author = is.object({
  name: randomString,
  age: is.number()
});
 
const schema = { author };

Builders

The purpose of Zaha is to create configurable builders. The zaha function converts a schema into a builder class that can be instantiated, like so:

const Builder = zaha(schema);
const builder = new Builder();

Builders define two function types:

• with<PropertyName>(value): Sets the value of the given property to the given argument
• build(): Emits an object with the values provided by with

A with function is generated for each first-order property defined in the schema. You can chain them like so:

const room = new RoomBuilder()
  .withWidth(100)
  .withLength(200)
  .build();

Note on property names

• Snake-cased property names, like last_name, will end up with a with function like withLast_name
• Property names which contain arbitrary symbols, like is-admin?, are not supported

Extending Builders

Zaha emits a class which can be extended. If you want to define custom methods on the builder, it's simple to do:

const Base = zaha({
  furniture: is.arrayOf(is.string())
});
 
export default class RoomBuilder extends Base {
  withoutFurniture() {
    this.schema.furniture = is([]);
    return this;
  }
}

Example

Here is a full use-case example. Chai is being used here, but any testing framework works with Zaha.

// room-builder.js
import zaha, { is } from 'zaha';
 
export default zaha({
  length: is.number(),
  width: is.number(),
  furniture: is.arrayOf(is.string())
});

import { expect } from 'chai';
import RoomBuilder from './room-builder';
import { moveAllFurniture } from './room-utils';
 
describe('Furniture Mover', () => {
  it('moves all furniture from one room into the other', () => {
    const furniture = ['chair', 'table'];
    const formerRoom = new RoomBuilder()
      .withFurniture(furniture)
      .build();
    const newRoom = new RoomBuilder()
      .withFurniture([])
      .build();
 
    moveAllFurniture.from(formerRoom).to(newRoom);
 
    expect(formerRoom.furniture).to.be.empty;
    expect(newRoom.furniture).to.deep.equal(furniture);
  });
});