Defer capturing original matchers

[jcarlson]

Referring to this code snippet: https://github.com/PsychoLlama/expect-enzyme/blob/master/src/assertions.js#L120-L145

This creates a problem, because definitions for any original matchers are captured at the time this module is imported or required rather than at the time expect is extended. This can be problematic when used alongside app-specific matchers with colliding names.

For example, the following does not work:

// test/helpers/my-matchers.js
export function toHaveClass(className) { ... }
export function toNotHaveClass(className) { ... }

// test/setup.js
import expect from 'expect'
import myMatchers from './helpers/my-matchers'
import enzymeMatchers from 'expect-enzyme'

expect.extend(myMatchers)
expect.extend(enzymeMatchers)

In the above example, as soon as expect-enzyme is imported, it captures any existing matchers, but they haven't been extended onto expect yet. It is a syntax error to move the import statement for enzyme-expect lower in the file, as all import statements must be at the top.

This can be worked around using require syntax as follows:

// test/setup.js
import expect from 'expect'

const myMatchers = require('./helpers/my-matchers')
expect.extend(myMatchers)

const enzymeMatchers = require('expect-enzyme')
expect.extend(enzymeMatchers)

This second form allows expect to be extended with the app-specific matchers before requireing the expect-enzyme matchers. While this work-around is okay for my current use case, it might be more problematic if another module included enzyme-expect before the test setup module.

Just thought you'd like to know.

[PsychoLlama]

That's a good point @jcarlson, import statements usually go at the top. If people are using multiple extensions for expect, the assertion overloading won't work.

What if expect-enzyme exported a function instead?

import enzymeMatchers from 'expect-enzyme'
import customMatchers from './helpers/my-matchers'

expect.extend(customMatchers)
expect.extend(enzymeMatchers()) // invocation captures existing assertions

It wouldn't be able to see any extensions added afterwards, but it would solve the import dilemma.

[PsychoLlama]

I've released v1.0 which exports a function. Instead of capturing the matchers on import, now it waits until it's invoked. That should help keep the import statements prettier 😉