Chai assertions for Facebook's Immutable library for JavaScript collections
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Chai Immutable

This plugin provides a set of Chai assertions for Facebook's Immutable library for JavaScript collections.

Installation

Node.js

Install via npm or yarn:

npm install --save-dev chai-immutable
yarn add --dev chai-immutable

⚠️ To use chai-immutable with Chai v4, you need to use npm install --save-dev chai-immutable@next (or yarn add --dev chai-immutable@next) instead, until I am done with the v2 release of this plugin. I apologize for the inconvenience in the meantime.

You can then use this plugin as any other Chai plugins:

const chai = require('chai');
const chaiImmutable = require('chai-immutable');

chai.use(chaiImmutable);

ES6 syntax (needs Babel transpiling)

import chai from 'chai';
import chaiImmutable from 'chai-immutable';

chai.use(chaiImmutable);

In the browser

Include this plugin after including Chai and Immutable. It will automatically plug in to Chai and be ready for use:

<script src="chai-immutable.js"></script>

Using chai-immutable with other plugins

If you are using this plugin with chai-as-promised or dirty-chai, note that chai-immutable must be loaded before any of them. For example:

const chai = require('chai');
const chaiAsPromised = require('chai-as-promised');
const chaiImmutable = require('chai-immutable');
const dirtyChai = require('dirty-chai');
const { expect } = chai;

chai.use(chaiImmutable);
chai.use(chaiAsPromised);
chai.use(dirtyChai);

const { List } = require('immutable');

/* ... */

expect(Promise.resolve(List.of(1, 2, 3))).to.eventually.have.size(3);
expect(true).to.be.true();

BDD API Reference

.empty

Asserts that the immutable collection is empty.

expect(List()).to.be.empty;
expect(List.of(1, 2, 3)).to.not.be.empty;

.equal(collection)

  • @param { Collection } collection

Asserts that the values of the target are equivalent to the values of collection. Aliases of Chai's original equal method are also supported.

const a = List.of(1, 2, 3);
const b = List.of(1, 2, 3);
expect(a).to.equal(b);

Immutable data structures should only contain other immutable data structures (unlike Arrays and Objects) to be considered immutable and properly work against .equal(). See this issue for more information.

Also, note that deep.equal and eql are synonyms of equal when tested against immutable data structures, therefore they are aliases to equal.

.include(value)

  • @param { Mixed } val

The include and contain assertions can be used as either property based language chains or as methods to assert the inclusion of a value in an immutable collection. When used as language chains, they toggle the contains flag for the keys assertion.

Note that deep.include behaves exactly like include in the context of immutable data structures.

expect(new List([1, 2, 3])).to.include(2);
expect(new List([1, 2, 3])).to.deep.include(2);
expect(new Map({ foo: 'bar', hello: 'world' })).to.include.keys('foo');

.keys(key1[, key2[, ...]])

  • @param { String... | Array | Object | Collection } keyN

Asserts that the target collection has the given keys.

When the target is an object or array, keys can be provided as one or more string arguments, a single array argument, a single object argument, or an immutable collection. In the last 2 cases, only the keys in the given object/collection matter; the values are ignored.

expect(new Map({ foo: 1, bar: 2 })).to.have.all.keys('foo', 'bar');
expect(new Map({ foo: 1, bar: 2 })).to.have.all.keys(new List(['bar', 'foo']));
expect(new Map({ foo: 1, bar: 2 })).to.have.all.keys(new Set(['bar', 'foo']));
expect(new Map({ foo: 1, bar: 2 })).to.have.all.keys(new Stack(['bar', 'foo']));
expect(new List(['x', 'y'])).to.have.all.keys(0, 1);

expect(new Map({ foo: 1, bar: 2 })).to.have.all.keys(['foo', 'bar']);
expect(new List(['x', 'y'])).to.have.all.keys([0, 1]);

// Values in the passed object are ignored:
expect(new Map({ foo: 1, bar: 2 })).to.have.all.keys({ bar: 6, foo: 7 });
expect(new Map({ foo: 1, bar: 2 })).to.have.all.keys(
  new Map({ bar: 6, foo: 7 })
);
expect(new List(['x', 'y'])).to.have.all.keys({ 0: 4, 1: 5 });

Note that deep.property behaves exactly like property in the context of immutable data structures.

By default, the target must have all of the given keys and no more. Add .any earlier in the chain to only require that the target have at least one of the given keys. Also, add .not earlier in the chain to negate .keys. It's often best to add .any when negating .keys, and to use .all when asserting .keys without negation.

When negating .keys, .any is preferred because .not.any.keys asserts exactly what's expected of the output, whereas .not.all.keys creates uncertain expectations.

// Recommended; asserts that target doesn't have any of the given keys
expect(new Map({ a: 1, b: 2 })).to.not.have.any.keys('c', 'd');

// Not recommended; asserts that target doesn't have all of the given
// keys but may or may not have some of them
expect(new Map({ a: 1, b: 2 })).to.not.have.all.keys('c', 'd');

When asserting .keys without negation, .all is preferred because .all.keys asserts exactly what's expected of the output, whereas .any.keys creates uncertain expectations.

// Recommended; asserts that target has all the given keys
expect(new Map({ a: 1, b: 2 })).to.have.all.keys('a', 'b');

// Not recommended; asserts that target has at least one of the given
// keys but may or may not have more of them
expect(new Map({ a: 1, b: 2 })).to.have.any.keys('a', 'b');

Note that .all is used by default when neither .all nor .any appear earlier in the chain. However, it's often best to add .all anyway because it improves readability.

// Both assertions are identical
expect(new Map({ a: 1, b: 2 })).to.have.all.keys('a', 'b'); // Recommended
expect(new Map({ a: 1, b: 2 })).to.have.keys('a', 'b'); // Not recommended

Add .include earlier in the chain to require that the target's keys be a superset of the expected keys, rather than identical sets.

// Target object's keys are a superset of ['a', 'b'] but not identical
expect(new Map({ a: 1, b: 2, c: 3 })).to.include.all.keys('a', 'b');
expect(new Map({ a: 1, b: 2, c: 3 })).to.not.have.all.keys('a', 'b');

However, if .any and .include are combined, only the .any takes effect. The .include is ignored in this case.

// Both assertions are identical
expect(new Map({ a: 1 })).to.have.any.keys('a', 'b');
expect(new Map({ a: 1 })).to.include.any.keys('a', 'b');

The alias .key can be used interchangeably with .keys.

expect(new Map({ foo: 1 })).to.have.key('foo');

.property(path[, val])

  • @param { String | Array | Iterable } path
  • @param { Mixed } val (optional)

Asserts that the target has a property with the given path.

expect(new Map({ a: 1 })).to.have.property('a');

When val is provided, .property also asserts that the property's value is equal to the given val. val can be an immutable collection.

expect(new Map({ a: 1 })).to.have.property('a', 1);

Note that deep.property behaves exactly like property in the context of immutable data structures.

Add .nested earlier in the chain to enable dot- and bracket-notation when referencing nested properties. An immutable List can also be used as the starting point of a nested.property.

expect(Immutable.fromJS({ a: { b: ['x', 'y'] } })).to.have.nested.property(
  'a.b[1]'
);
expect(Immutable.fromJS({ a: { b: ['x', 'y'] } })).to.have.nested.property(
  'a.b[1]',
  'y'
);
expect(Immutable.fromJS({ a: { b: ['x', 'y'] } })).to.have.nested.property(
  ['a', 'b', 1],
  'y'
);
expect(Immutable.fromJS({ a: { b: ['x', 'y'] } })).to.have.nested.property(
  new List(['a', 'b', 1]),
  'y'
);

If . or [] are part of an actual property name, they can be escaped by adding two backslashes before them.

expect(Immutable.fromJS({ '.a': { '[b]': 'x' } })).to.have.nested.property(
  '\\.a.\\[b\\]'
);

Add .not earlier in the chain to negate .property.

expect(new Map({ a: 1 })).to.not.have.property('b');

However, it's dangerous to negate .property when providing val. The problem is that it creates uncertain expectations by asserting that the target either doesn't have a property at the given path, or that it does have a property at the given key path but its value isn't equal to the given val. It's often best to identify the exact output that's expected, and then write an assertion that only accepts that exact output.

When the target isn't expected to have a property at the given path, it's often best to assert exactly that.

expect(new Map({ b: 2 })).to.not.have.property('a'); // Recommended
expect(new Map({ b: 2 })).to.not.have.property('a', 1); // Not recommended

When the target is expected to have a property at the given key path, it's often best to assert that the property has its expected value, rather than asserting that it doesn't have one of many unexpected values.

expect(new Map({ a: 3 })).to.have.property('a', 3); // Recommended
expect(new Map({ a: 3 })).to.not.have.property('a', 1); // Not recommended

.property changes the target of any assertions that follow in the chain to be the value of the property from the original target object.

expect(new Map({ a: 1 }))
  .to.have.property('a')
  .that.is.a('number');

.size(value)

  • @param { Number } size

Asserts that the immutable collection has the expected size.

expect(List.of(1, 2, 3)).to.have.size(3);

It can also be used as a chain precursor to a value comparison for the size property.

expect(List.of(1, 2, 3)).to.have.size.least(3);
expect(List.of(1, 2, 3)).to.have.size.most(3);
expect(List.of(1, 2, 3)).to.have.size.above(2);
expect(List.of(1, 2, 3)).to.have.size.below(4);
expect(List.of(1, 2, 3)).to.have.size.within(2, 4);

Similarly to length/lengthOf, sizeOf is an alias of size:

expect(List.of(1, 2, 3)).to.have.sizeOf(3);

TDD API Reference

.equal(actual, expected)

  • @param { Collection } actual
  • @param { Collection } expected

Asserts that the values of actual are equivalent to the values of expected. Note that .strictEqual() and .deepEqual() assert exactly like .equal() in the context of Immutable data structures.

const a = List.of(1, 2, 3);
const b = List.of(1, 2, 3);
assert.equal(a, b);

Immutable data structures should only contain other immutable data structures (unlike Arrays and Objects) to be considered immutable and properly work against .equal(), .strictEqual() or .deepEqual(). See this issue for more information.

.notEqual(actual, expected)

  • @param { Collection } actual
  • @param { Collection } expected

Asserts that the values of actual are not equivalent to the values of expected. Note that .notStrictEqual() and .notDeepEqual() assert exactly like .notEqual() in the context of Immutable data structures.

const a = List.of(1, 2, 3);
const b = List.of(4, 5, 6);
assert.notEqual(a, b);

.sizeOf(collection, length)

  • @param { Collection } collection
  • @param { Number } size

Asserts that the immutable collection has the expected size.

assert.sizeOf(List.of(1, 2, 3), 3);
assert.sizeOf(new List(), 0);