js-test-utils

This package contains various utility methods that are useful for testing in a JavsScript environment.

Installation

npm install js-test-utils

Usage

Require the package

const TestUtil = require('js-test-utils');

and use any of the methods outlined below

Method Reference

IdentityClass

IdentityClass is a class property. Instantiating the class with a single argument passed to the constructor will set the instance's value property to the value of that argument.

const TestUtil = require('js-test-utils');

const myClass1 = new TestUtil.IdentityClass('Tax Loss Harvesting');
myClass1.value; // 'Tax Loss Harvesting

assertThrows

assertThrows takes a function reference and an expected error message, and asserts that the function throws an error. If an expected error message was provided, it will assert that the actual error message matches (deep equal).

const TestUtil = require('js-test-utils');

TestUtil.assertThrows(() => throw new Error('CAC 40'), 'CAC 40');
// This will not throw an error

TestUtil.assertThrows(() => throw new Error('CAC 40'));
// This will not throw an error

TestUtil.assertThrows(() => throw new Error('CAC 40'), 'ASX 100');
// This will throw an error

TestUtil.assertThrows(() => 'CAC 40', 'CAC 40');
// This will throw an error

assertDoesNotThrow

assertDoesNotThrow takes a function reference and an expected result, and asserts that the function does not throw an error. If an expected result was provided, it will assert that the actual result matches (deep equal).

const TestUtil = require('js-test-utils');

TestUtil.assertDoesNotThrow(() => 'CAC 40', 'CAC 40');
// This will not throw an error

TestUtil.assertDoesNotThrow(() => 'CAC 40');
// This will not throw an error

TestUtil.assertDoesNotThrow(() => 'CAC 40', 'ASX 100');
// This will throw an error

TestUtil.assertDoesNotThrow(() => throw new Error('CAC 40'), 'CA 40');
// This will throw an error

expectPromiseRejection

expectPromiseRejection takes a function which returns a promise and an expected rejection message, and asserts that the promise rejects. If an expected rejection message was provided, it will assert that the actual rejection message matches (deep equal). expectPromiseRejection returns a promise.

const TestUtil = require('js-test-utils');

TestUtil.expectPromiseRejection(() => Promise.reject('ASX 100'), 'ASX 100');
// This will resolve

TestUtil.expectPromiseRejection(() => Promise.reject('ASX 100'));
// This will resolve

TestUtil.expectPromiseRejection(() => Promise.reject('ASX 100'), 'CAC 40');
// This will reject

TestUtil.expectPromiseRejection(() => Promise.resolve('ASX 100'), 'ASX 100');
// This will reject

expectPromiseResolution

expectPromiseResolution takes a function which returns a promise and an expected resolution, and asserts that the promise resolves. If an expected resolution was provided, it will assert that the actual resolution matches (deep equal). expectPromiseResolution returns a promise.

const TestUtil = require('js-test-utils');

TestUtil.expectPromiseResolution(() => Promise.resolve('ASX 100'), 'ASX 100');
// This will resolve

TestUtil.expectPromiseResolution(() => Promise.resolve('ASX 100'));
// This will resolve

TestUtil.expectPromiseResolution(() => Promise.resolve('ASX 100'), 'CAC 40');
// This will reject

TestUtil.expectPromiseResolution(() => Promise.reject('ASX 100'), 'ASX 100');
// This will reject

mapValuesExcept

mapValuesExcept takes an initial object, variable to map to, and a list of exceptions. It returns a new object with the same keys as the initial object, but the values for the keys not in the exceptions array have been replaced by a copy of the variable to map to.

const TestUtil = require('js-test-utils');

TestUtil.mapValuesExcept({
    notes: 'foo',
    accounts: 13,
    salaries: undefined,
    wages: 14.01,
}, { an: 'object' }, ['salaries', 'wages', 'interest', 'taxes']);

/* {
 *     notes: { an: 'object' },
 *     accounts: { an: 'object' },
 *     salaries: undefined,
 *     wages: undefined,
 * }

suppressTestOutput

suppressTestOutput stubs properties on the global console object to prevent output. It takes a function reference and an optional list of console output types to stub, which defaults to ['log']. Note that because this method stubs methods on the console object, output via alternative methods (such as process.stdout.write) will not be suppressed.

const TestUtil = require('js-test-utils');

TestUtil.suppressTestOutput(() => {
    console.log('foo');
    console.warn('bar');
    console.error('baz');
}, ['log', 'warn']);
// Only 'baz' will be displayed in the console.

testClassIsNotInstantiable

testClassIsNotInstantiable attempts to instantiate the given class with one argument: {}. It asserts that this throws the error "${ClassRef.name} is not instantiable."

const TestUtil = require('js-test-utils');

class NonInstantiableClass1 {
    constructor (obj) {
        throw new Error('NonInstantiableClass1 is not instantiable');
    }
}

class NonInstantiableClass2 {
    constructor (obj) {
        throw new Error('Another error message');
    }
}

TestUtil.testClassIsNotInstantiable(NonInstantiableClass1);
// This will not throw an error

TestUtil.testClassIsNotInstantiable(NonInstantiableClass2);
// This will throw an error

TestUtil.testClassIsNotInstantiable(class {});
// This will throw an error

testSubclassIsInstantiable

testClassIsNotInstantiable attempts to instantiate a subclass of the given class with one argument: {}. It asserts that this does not throw an error. By default, the subclass is automatically derived, although it can also be explicitly provided as the second argument.

const TestUtil = require('js-test-utils');

class NonInstantiableClass1 {
    constructor (obj) {
        throw new Error('NonInstantiableClass1 is not instantiable');
    }
}

class NonInstantiableClass2 {
    constructor (obj) {
        if ('NonInstantiableClass2' === this.constructor.name)
            throw new Error('Another error message');
    }
}

TestUtil.testSubclassIsInstantiable(NonInstantiableClass1, class {});
// This will not throw an error

TestUtil.testSubclassIsInstantiable(NonInstantiableClass2);
// This will not throw an error

TestUtil.testSubclassIsInstantiable(NonInstantiableClass1);
// This will throw an error