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jest-webgl-canvas-mock
Advanced tools
Readme
Mock
canvas
andWebGL
when running unit test cases with jest.
This project is a simple merge of jest-canvas-mock with webgl-mock so that both 2d and webgl contexts can be tested in jest. As such, the only tests provided are those from the original projects.
The current goal of this project is simply to make any tests using pixi.js
work in jest.
Please feel free to contribute and add any additional functionality required.
This should only be installed as a development dependency (devDependencies
) as it is only designed for testing.
npm i --save-dev jest-webgl-canvas-mock
In your package.json
under the jest
, create a setupFiles
array and add jest-webgl-canvas-mock
to the array.
{
"jest": {
"setupFiles": ["jest-webgl-canvas-mock"]
}
}
If you already have a setupFiles
attribute you can also append jest-webgl-canvas-mock
to the array.
{
"jest": {
"setupFiles": ["./__setups__/other.js", "jest-webgl-canvas-mock"]
}
}
More about in configuration section.
Alternatively you can create a new setup file which then requires this module or
add the require
statement to an existing setup file.
__setups__/canvas.js
import 'jest-webgl-canvas-mock';
// or
require('jest-webgl-canvas-mock');
Add that file to your setupFiles
array:
"jest": {
"setupFiles": [
"./__setups__/canvas.js"
]
}
This mock strategy implements all the canvas functions and actually verifies the parameters. If a
known condition would cause the browser to throw a TypeError
or a DOMException
, it emulates the
error. For instance, the CanvasRenderingContext2D#arc
function will throw a TypeError
if the
radius is negative, or if it was not provided with enough parameters.
// arc throws a TypeError when the argument length is less than 5
expect(() => ctx.arc(1, 2, 3, 4)).toThrow(TypeError);
// when radius is negative, arc throws a dom exception when all parameters are finite
expect(() => ctx.arc(0, 0, -10, 0, Math.PI * 2)).toThrow(DOMException);
The function will do Number
type coercion and verify the inputs exactly like the browser does. So
this is valid input.
expect(() => ctx.arc("10", "10", "20", "0", "6.14")).not.toThrow();
Another part of the strategy is to validate input types. When using the
CanvasRenderingContext2D#fill
function, if you pass it an invalid fillRule
it will throw a
TypeError
just like the browser does.
expect(() => ctx.fill("invalid!")).toThrow(TypeError);
expect(() => ctx.fill(new Path2D(), "invalid!")).toThrow(TypeError);
We try to follow the ECMAScript specification as closely as possible.
There are multiple ways to validate canvas state. There are currently three static
methods attached
to the CanvasRenderingContext2D
class. The first way to use this feature is by using the __getEvents
method.
/**
* In order to see which functions and properties were used for the test, you can use `__getEvents`
* to gather this information.
*/
const events = ctx.__getEvents();
expect(events).toMatchSnapshot(); // jest will assert the events match the snapshot
The second way is to inspect the current path associated with the context.
ctx.beginPath();
ctx.arc(1, 2, 3, 4, 5);
ctx.moveTo(6, 7);
ctx.rect(6, 7, 8, 9);
ctx.closePath();
/**
* Any method that modifies the current path (and subpath) will be pushed to an event array. When
* using the `__getPath` method, that array will sliced and usable for snapshots.
*/
const path = ctx.__getPath();
expect(path).toMatchSnapshot();
The third way is to inspect all of the success draw calls submitted to the context.
ctx.drawImage(img, 0, 0);
/**
* Every drawImage, fill, stroke, fillText, or strokeText function call will be logged in an event
* array. This method will return those events here for inspection.
*/
const calls = ctx.__getDrawCalls();
expect(calls).toMatchSnapshot();
You can override the default mock return value in your test to suit your need. For example, to override return value of toDataURL
:
canvas.toDataURL.mockReturnValueOnce(
'data:image/png;base64, iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg=='
);
MIT
FAQs
Mock both 2D and WebGL contexts in Jest.
We found that jest-webgl-canvas-mock demonstrated a healthy version release cadence and project activity because the last version was released less than a year ago. It has 1 open source maintainer collaborating on the project.
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