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https://github.com/binarymuse/babel-plugin-chai-assert-async
Convert synchronous chai assertions into asynchronous chai assertions
https://github.com/binarymuse/babel-plugin-chai-assert-async
assertions chai testing
Last synced: 2 months ago
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Convert synchronous chai assertions into asynchronous chai assertions
- Host: GitHub
- URL: https://github.com/binarymuse/babel-plugin-chai-assert-async
- Owner: BinaryMuse
- Created: 2017-06-09T21:14:01.000Z (over 7 years ago)
- Default Branch: master
- Last Pushed: 2017-06-09T21:45:29.000Z (over 7 years ago)
- Last Synced: 2024-11-30T08:41:26.246Z (2 months ago)
- Topics: assertions, chai, testing
- Language: JavaScript
- Homepage:
- Size: 21.5 KB
- Stars: 0
- Watchers: 2
- Forks: 5
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
Awesome Lists containing this project
README
# babel-plugin-chai-assert-async
Transforms `assert.async.*` calls into `test-until` expressions that resolve when the assertion passes, preserving error messages for failed assertions.
[](https://travis-ci.org/BinaryMuse/babel-plugin-chai-assert-async)
## Installation
Assuming you're [already using Babel](http://babeljs.io/docs/setup/), install the Babel plugin *and the peer dependency* with your package manager of choice:
```sh
$ npm install babel-plugin-chai-assert-async test-until
```
## Usage
### Via `.babelrc`
**.babelrc**
```json
{
"plugins": ["chai-assert-async"]
}
```
### Via CLI
```sh
$ babel --plugins chai-assert-async script.js
```
### Via Node API
```javascript
require("babel-core").transform("code", {
plugins: ["chai-assert-async"]
});
```
## Details
During tests, it's sometime's useful to test values that are set asynchronously, or to wait for a condition to be true before continuing the test. Here's a convoluted example:
```javascript
function setValueAsync(obj) {
setTimeout(() => obj.val = 42, 100)
}
describe('setValueAsync', function() {
it('sets a value asynchronously', function() {
const obj = {val: 0}
setValueAsync(obj)
assert.equal(obj.val, 42) // will fail
})
})
```
This test will fail because `obj.val` does not equal `42` at the time the assertion is run.
We can use [a library like `test-until`](https://www.npmjs.com/package/test-until) to ensure the test doesn't continue until `obj.val` does equal `42`. Here's an example with Mocha, `async`/`await`
```javascript
import until from 'test-until'
// ....
it('sets a value asynchronously', function() {
const obj = {val: 0}
setValueAsync(obj)
await until(() => obj.val === 42)
})
```
However, in converting from the `assert.equal` version of this test to the `await until` version, we lost some information. In particular, it's more difficult to know exactly what we're testing, and if the `until` expression times out, we get a very generic error message like "timed out waiting for something to happen" instead of something useful like "expected obj.val to equal 42".
This transform allows you to convert something like `assert.equal(obj.val, 42)` into an equivalent `until` expression by writing `assert.async.equal(obj.val, 42)`:
```javascript
function setValueAsync(obj) {
setTimeout(() => obj.val = 42, 100)
}
describe('setValueAsync', function() {
it('sets a value asynchronously', async function() {
const obj = {val: 0}
setValueAsync(obj)
await assert.async.equal(obj.val, 42)
})
})
```
In this case, if the async assertion fails, the original error message like "expected obj.val to equal 42" will be preserved.
If you want to pass a timeout to `test-until`, you can specify it as an argument to `async`:
```javascript
await assert.async(100).equal(obj.val, 42)
```
## Examples
**Basic**
In
```js
async function test() {
await assert.async.equal(thing, other);
}
```
Out
```js
"use strict";
import until from 'test-until';
async function test() {
await until(async function (fail) {
try {
assert.equal(thing, other);
return true;
} catch (err) {
return fail(err);
}
});
}
```
**With explicit timeout**
In
```js
async function test() {
await assert.async(500).equal(thing, other);
}
```
Out
```js
"use strict";
import until from 'test-until';
async function test() {
await until(async function (fail) {
try {
assert.equal(thing, other);
return true;
} catch (err) {
return fail(err);
}
}, 500);
}
```