Natural Performance Manager


    0.8.0 • Public • Published


    An easy way to generate test data for your JavaScript unit tests. Completely agnostic of test runner, framework or environment.

    npm install --save-dev test-data-bot
    const { build, fake, sequence } = require('test-data-bot')
    const userBuilder = build('User').fields({
      name: fake(f =>,
      email: sequence(x => `jack${x}`),
      age: 26,
    const user = userBuilder()
    // => { name: 'Bob Fleming', email: '', age: 26 }


    Firstly, use build to create a new builder. The name passed is just for debugging/documentation purposes and can be whatever you'd like.

    Once you've created a builder, use fields to pass in the names and values of fields.

    Field values can be one of:

    • A static value, in which case any generated data from this builder will always use that value.
    • A call to sequence, which takes a function which is passed a number. This is an easy way to ensure a value is unique everytime, but still know what it will be. A sequence is per field, and the number starts at 1.
    • A call to fake. This takes a function that will be called with an instance of faker.js, and you can use any of the faker API methods to return data.
    • A call to perBuild. This takes a function that will be called each time an instance is created. This is useful if you want each instance to have the same actual value (say, an object), but one that isn't referentially the same.
    • A call to incrementingId. This will produce a number that starts at 1 and increments each time it is used. Good to model IDs from a database.
    • A call to oneOf. This takes any number of primitive values, and picks one at random.
    • A call to arrayOf. This takes any value (including another builder) and generates an array of them. It also takes the array length as the second argument: arrayOf('foo', 2) will generate ['foo', 'foo']. arrayOf(fake(f =>, 5) will generate an array of 5 random names.
    • A call to bool. This is a shortcut for oneOf(true, false) and will pick one of them at random.
    • A call to numberBetween. This takes two arguments as min/max, and generates a random integer between them. numberBetween(0, 10) is a shortcut for fake(f => f.random.number({ min: 0, max: 10 }).


    The test-data-bot always creates plain JavaScript objects, but you may need to generate instances of a class, for example. In this instance, you can pass a map to the builder. This will be called with the generated object, and you can then do with that data whatever you'd like:

    const userBuilder = build('User')
        name: fake(f =>,
        email: sequence(x => `jack${x}`),
      .map(user => ({
    const user = userBuilder()
    // => { name: 'BOB FLEMING', email: 'JACK1@TEST.COM' }

    Hard coding values and overriding

    Sometimes you might want to ensure a certain value, rather than use the generator. In this case you can pass it in when you call the builder:

    const userBuilder = build('User').fields({
      name: fake(f =>,
      email: sequence(x => `jack${x}`),
    const user = userBuilder({ name: 'JACK' })
    // => { name: 'JACK', email: '' }

    In this case, name will always be 'JACK', and the generator given will not be used.


    npm i test-data-bot

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    • jackfranklin