bdd-lazy-var
v2.6.1
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Provides "ui" for testing frameworks such as mocha/jasmine which allows to define lazy variables and subjects
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BDD + lazy variable definition (aka rspec)
Provides "ui" for testing frameworks such as mocha, jasmine and jest which allows to define lazy variables and subjects.
Purpose
The old way
describe('Suite', function() {
var name;
beforeEach(function() {
name = getName();
});
afterEach(function() {
name = null;
});
it('uses name variable', function() {
expect(name).to.exist;
});
it('does not use name but anyway it is created in beforeEach', function() {
expect(1).to.equal(1);
});
});
Why should it be improved?
Because as soon as amount of your tests increase, this pattern became increasingly difficult.
Sometimes you will find yourself jumping around spec files, trying to find out where a given variable was initially defined.
Or even worst, you may run into subtle bugs due to clobbering variables with common names (e.g. model
, view
) within a given scope, failing to realize they had already been defined.
Furthermore, declaration statements in describe
blocks will start looking something like:
var firstVar, secondVar, thirdVar, fourthVar, fifthVar, ..., nthVar
This is ugly and hard to parse. Finally, you can sometimes run into flaky tests due to "leaks" - test-specific variables that were not properly cleaned up after each case.
The new, better way
In an attempt to address these issues, I had with my e2e tests, I decided to create this library, which allows to define suite specific variables in more elegant way. So the original code above looks something like this:
describe('Suite', () => {
def('name', () => `John Doe ${Math.random()}`);
it('defines `name` variable', () => {
expect($name).to.exist
});
it('does not use name, so it is not created', () => {
expect(1).to.equal(1);
});
});
Why the new way rocks
Switching over to this pattern has yielded a significant amount of benefits for us, including:
No more global leaks
Because lazy vars are cleared after each test, we didn't have to worry about test pollution anymore. This helped ensure isolation between our tests, making them a lot more reliable.
Clear meaning
Every time I see a $<variable>
reference in my tests, I know where it's defined.
That, coupled with removing exhaustive var
declarations in describe
blocks, have made even my largest tests clear and understandable.
Lazy evaluation
Variables are instantiated only when referenced. That means if you don't use variable inside your test it won't be evaluated, making your tests to run faster. No useless instantiation any more!
Composition
Due to laziness we are able to compose variables. This allows to define more general varibles at the top level and more specific at the bottom:
describe('User', function() {
subject('user', () => new User($props))
describe('when user is "admin"', function() {
def('props', () => ({ role: 'admin' }))
it('can update articles', function() {
// user is created with property role equal "admin"
expect($user).to....
})
})
describe('when user is "member"', function() {
def('props', () => ({ role: 'member' }))
it('cannot update articles', function() {
// user is created with property role equal "member"
expect($user).to....
})
})
})
Tests reusage
Very often you may find that some behavior repeats (e.g., when you implement Adapter pattern), and you would like to reuse tests for a different class or object. To do this Wiki of Mocha.js recommend to move your tests into separate function and call it whenever you need it.
I prefer to be more explicit in doing this, that's why created few helper methods:
sharedExamplesFor
- defines a set of reusable tests. When you call this function, it just stores your testsincludeExamplesFor
- runs previously defined examples in current context (i.e., in currentdescribe
)itBehavesLike
- runs defined examples in nested context (i.e., in nesteddescribe
)
sharedExamplesFor
defines shared examples in the scope of the currently defining suite.
If you call this function outside describe
(or context
) it defines shared examples globally.
WARNING: files containing shared examples must be loaded before the files that use them.
Scenarios
sharedExamplesFor('a collection', () => {
it('has three items', () => {
expect($subject.size).to.equal(3)
})
describe('#has', () => {
it('returns true with an item that is in the collection', () => {
expect($subject.has(7)).to.be.true
})
it('returns false with an item that is not in the collection', () => {
expect($subject.has(9)).to.be.false
})
})
})
describe('Set', () => {
subject(() => new Set([1, 2, 7]))
itBehavesLike('a collection')
})
describe('Map', () => {
subject(() => new Map([[2, 1], [7, 5], [3, 4]]))
itBehavesLike('a collection')
})
sharedExamplesFor('a collection', (size, existingItem, nonExistingItem) => {
it('has three items', () => {
expect($subject.size).to.equal(size)
})
describe('#has', () => {
it('returns true with an item that is in the collection', () => {
expect($subject.has(existingItem)).to.be.true
})
it('returns false with an item that is not in the collection', () => {
expect($subject.has(nonExistingItem)).to.be.false
})
})
})
describe('Set', () => {
subject(() => new Set([1, 2, 7]))
itBehavesLike('a collection', 3, 2, 10)
})
describe('Map', () => {
subject(() => new Map([[2, 1]]))
itBehavesLike('a collection', 1, 2, 3)
})
There are 2 ways how to pass lazy variables:
- all variables are inherited by nested contexts (i.e.,
describe
calls), so you can rely on variable name, as it was done withsubject
in previous examples - you can pass variable definition using
get.variable
helper
sharedExamplesFor('a collection', (collection) => {
def('collection', collection)
it('has three items', () => {
expect($collection.size).to.equal(1)
})
describe('#has', () => {
it('returns true with an item that is in the collection', () => {
expect($collection.has(7)).to.be.true
})
it('returns false with an item that is not in the collection', () => {
expect($collection.has(9)).to.be.false
})
})
})
describe('Set', () => {
subject(() => new Set([7]))
itBehavesLike('a collection', get.variable('subject'))
})
describe('Map', () => {
subject(() => new Map([[2, 1]]))
itBehavesLike('a collection', get.variable('subject'))
})
Shortcuts
Very often we want to declare several test cases which tests subject's field or subject's behavior.
To do this quickly you can use its
or it
without message:
describe('Array', () => {
subject(() => ({
items: [1, 2, 3],
name: 'John'
}))
its('items.length', () => is.expected.to.equal(3)) // i.e. expect($subject.items.length).to.equal(3)
its('name', () => is.expected.to.equal('John')) // i.e. expect($subject.name).to.equal('John')
// i.e. expect($subject).to.have.property('items').which.has.length(3)
it(() => is.expected.to.have.property('items').which.has.length(3))
})
Also it generates messages for you based on passed in function body. The example above reports:
Array
✓ is expected to have property('items') which has length(3)
items.length
✓ is expected to equal(3)
name
✓ is expected to equal('John')
Note: if you use mocha
and chai
make sure that defines global.expect = chai.expect
, otherwise is.expected
will throw error that context.expect
is undefined
.
Installation
npm install bdd-lazy-var --save-dev
Command line
mocha -u bdd-lazy-var/global
In JavaScript
See Using Mocha programatically
const Mocha = require('mocha');
const mocha = new Mocha({
ui: 'bdd-lazy-var/global' // bdd-lazy-var or bdd-lazy-var/getter
});
mocha.addFile(...)
mocha.run(...)
// !!! Important the next code should be written in a separate file
// later you can either use `get` and `def` as global functions
// or export them from corresponding module
const { get, def } = require('bdd-lazy-var/global');
describe('Test', () => {
// ...
})
Using karma (via karma-mocha npm package)
Note requires karma-mocha
^1.1.1
So, in karma.config.js
it looks like this:
module.exports = function(config) {
config.set({
// ....
client: {
mocha: {
ui: 'bdd-lazy-var/global',
require: [require.resolve('bdd-lazy-var/global')]
}
}
});
}
Command line
jasmine --helper=node_modules/bdd-lazy-var/global.js
or using spec/spec_helper.js
require('bdd-lazy-var/global');
// ... other helper stuff
and then
jasmine --helper=spec/*_helper.js
In JavaScript
When you want programatically run jasmine
require('jasmine-core');
// !!! Important the next code should be written in a separate file
// later you can either use `get` and `def` as global functions
// or export them from corresponding module
const { get, def } = require('bdd-lazy-var/global');
describe('Test', () => {
// ...
})
Using karma (via karma-jasmine npm package)
So, in karma.config.js
it looks like this:
module.exports = function(config) {
config.set({
// ....
files: [
'node_modules/bdd-lazy-var/global.js',
// ... your specs here
]
});
}
Command line
Use Jest as usually if you export get
and def
from corresponding module
jest
In case you want to use global get
and def
jest --setupTestFrameworkScriptFile bdd-lazy-var/global
In JavaScript
// later you can either use `get` and `def` as global functions
// or export them from relative module
const { get, def } = require('bdd-lazy-var/global');
Dialects
bdd-lazy-var
provides 3 different dialects:
- access variables by referencing
$<variableName>
(the recommended one, available by requiringbdd-lazy-var/global
) - access variables by referencing
get.<variableName>
(more strict, available by requiringbdd-lazy-var/getter
) - access variables by referencing
get('<variableName>')
(the most strict and less readable way, available by requiringbdd-lazy-var
)
All are bundled as UMD versions. Each dialect is compiled in a separate file and should be required or provided for testing framework.
Aliases
In accordance with Rspec's DDL, context
, xcontext
, and fcontext
have been aliased to their related describe
commands for both the Jest and Jasmine testing libraries. Mocha's BDD interface already provides this keyword.
The Core Features
- lazy instantiation, allows variable composition
- automatically cleaned after each test
- accessible inside
before/beforeAll
,after/afterAll
callbacks - named
subject
s to be more explicit - ability to shadow parent's variable
- variable inheritance with access to parent variables
- supports typescript
For more information, read the article on Medium.
TypeScript Notes
It's also possible to use bdd-lazy-var
with TypeScript. The best integrated dialects are get
and getter
. To do so, you need either include corresponding definitions in your tsconfig.json or use ES6 module system.
{
"compilerOptions": {
"module": "commonjs",
"removeComments": true,
"preserveConstEnums": true,
"sourceMap": true
},
"include": [
"src/**/*",
"node_modules/bdd-lazy-var/index.d.ts" // for `get('<variableName>')` syntax
// or
"node_modules/bdd-lazy-var/getter.d.ts" // for `get.<variableName>` syntax
]
}
import { get, def } from 'bdd-lazy-var'
// or
import { get, def } from 'bdd-lazy-var/getter'
describe('My Test', () => {
// ....
})
In this case TypeScript loads corresponding declarations automatically
It's a bit harder to work with global
dialect. It creates global getters on the fly, so there is no way to let TypeScript know something about these variables, thus you need to declare
them manually.
import { def } from 'bdd-lazy-var/global'
describe('My Test', () => {
declare let $value: number // <-- need to place this declarations manually
def('value', () => 5)
it('equals 5', () => {
expect($value).to.equal(5)
})
})
As with other dialects you can either use import
statements to load typings automatically or add them manually in tsconfig.json
Examples
describe('Array', () => {
subject(() => [1, 2, 3]);
it('has 3 elements by default', () => {
expect($subject).to.have.length(3);
});
});
describe('Array', () => {
subject('collection', () => [1, 2, 3]);
it('has 3 elements by default', () => {
expect($subject).to.equal($collection);
expect($collection).to.have.length(3);
});
});
describe('Array', () => {
subject('collection', () => [1, 2, 3]);
beforeEach(() => {
// this beforeEach is executed for tests of suite with subject equal [1, 2, 3]
// and for nested describe with subject being []
$subject.push(4);
});
it('has 3 elements by default', () => {
expect($subject).to.equal($collection);
expect($collection).to.have.length(3);
});
describe('when empty', () => {
subject(() => []);
it('has 1 element', () => {
expect($subject).not.to.equal($collection);
expect($collection).to.deep.equal([4]);
});
});
});
describe('Array', () => {
subject('collection', () => [1, 2, 3]);
it('has 3 elements by default', () => {
expect($subject).to.equal($collection);
expect($collection).to.have.length(3);
});
describe('when empty', () => {
subject(() => {
// in this definition `$subject` references parent $subject (i.e., `$collection` variable)
return $subject.concat([4, 5]);
});
it('is properly uses parent subject', () => {
expect($subject).not.to.equal($collection);
expect($collection).to.deep.equal([1, 2, 3, 4, 5]);
});
});
});
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