True
-
To make true; shape, adjust, place, etc., exactly or accurately:
True the wheels of a bicycle after striking a pothole.
-
To make even, symmetrical, level, etc. (often followed by up):
True up the sides of a door.
-
To test your Sass code; debug, perfect, etc. (often using True):
True your sweet plugin before you deploy.
True is a unit-testing tool for Sass code. All of the tests are written in plain Sass, and can be compiled using Dart Sass – but we also provide integration with JavaScript test runners (e.g. Mocha or Jest), for extra features and improved reporting.
Install
In command line:
npm install --save-dev sass-true
Import in your test directory, like any other Sass file:
@use 'true' as *;
Depending on your setup, you may need to include the full path name:
// This is only an example, your path may be different
@use '../node_modules/sass-true' as *;
One Setting
$terminal-output
(boolean),
defaults to true
true
will show detailed information in the terminal for debugging failed assertions or reporting final results. This is the default, and best for compiling without a JavaScript test runner.false
will turn off all terminal output from Sass, though Mocha/Jest will continue to use the terminal for reporting.
If you are still using @import
rather than @use
,
there is an import path available -
which retains the legacy prefixed $true-terminal-output
variable name:
// Your path may be different
@import '../node_modules/sass-true/sass/true';
Usage
True is based on common JS-testing patterns,
allowing both a test-module
/test
syntax,
and the newer describe
/it
for defining the structure:
@include test-module('Zip [function]') {
@include test('Zips multiple lists into a single multi-dimensional list') {
// Assert the expected results
@include assert-equal(zip(a b c, 1 2 3), (a 1, b 2, c 3));
}
}
This is the same as…
@include describe('Zip [function]') {
@include it('Zips multiple lists into a single multi-dimensional list') {
// Assert the expected results
@include assert-equal(zip(a b c, 1 2 3), (a 1, b 2, c 3));
}
}
Sass is able to compare values internally, meaning function-output and variable values can easily be compared and reported during Sass compilation.
CSS output tests, on the other hand,
have to be compared after compilation is complete.
You can do that by hand if you want
(git diff
is helpful for noticing changes),
or you can use a test runner
such as Mocha or Jest.
Output tests fit the same structure,
but assertions take a slightly different form,
with an outer assert
mixin,
and a matching pair of output
and expect
to contain the output-values.
// Test CSS output from mixins
@include it('Outputs a font size and line height based on keyword') {
@include assert {
@include output {
@include font-size('large');
}
@include expect {
font-size: 2rem;
line-height: 3rem;
}
}
}
You can optionally show a summary report in CSS and/or the command line, after the tests have completed:
@include report;
See the full documentation online for more details. See CHANGELOG.md when upgrading from an older version of True.
Using Mocha, Jest, or other JS test runners
-
Install
true
via npm:npm install --save-dev sass-true
-
[Optional] Install
sass
(Dart Sass), if not already installed.npm install --save-dev sass
-
Write some Sass tests in
test/test.scss
(see above). -
Write a shim JS test file in
test/sass.test.js
:const path = require('path'); const sassTrue = require('sass-true'); const sassFile = path.join(__dirname, 'test.scss'); sassTrue.runSass({ describe, it }, sassFile);
-
Run Mocha/Jest, and see your Sass tests reported in the command line.
Note: Because of differences between Jest globals and Node globals, Dart
Sass often errors when trying to compile in a Jest environment (e.g.
J.getInterceptor$ax(...).map$1$1 is not a function
). This can usually be fixed
by installing
jest-environment-node-single-context
and setting testEnvironment: 'jest-environment-node-single-context'
in
jest.config.js
. See possible
related
issues.
Note: Jest does not watch for changes in Sass files by default. To use
jest --watch
with True, add "scss" to your
moduleFileExtensions
setting.
You can call runSass
more than once, if you have multiple Sass test files you
want to run separately.
The first argument is an object with required describe
and it
options, and
optional contextLines
and sourceType
options.
Any JS test runner with equivalents to Mocha's or Jest's describe
and it
should be usable in the same way: just pass your test runner's describe
and
it
equivalents in the first argument to runSass
.
If True can't parse the CSS output, it'll give you some context lines of CSS as
part of the error message. This context will likely be helpful in understanding
the parse failure. By default it provides up to 10 lines of context; if you need
more, you can provide a numeric contextLines
option: the maximum number of
context lines to provide.
The second argument is a string representing either the path to a source Sass
file (passed through to Sass'
compile
function), or a string of source Sass (passed through to Sass'
compileString
function). By default it is expected to be a path, and sass.compile
is used --
to pass in a source string (and use sass.compileString
), add sourceType: 'string'
to your options passed in as the first argument to runSass
.
The third (optional) argument to runSass
accepts the same
options that
Sass' compile
or compileString
expect, and these are passed directly through
to Sass. The only modification runSass
makes is to add True's sass path to the
loadPaths
option, so @use 'true';
works in your Sass test file.
Note: True requires the
default Sass 'expanded'
output style,
and will not work if { style: 'compressed' }
is used in the third argument to
runSass
.
Custom Importers
If you use Webpack's tilde notation, like @use '~accoutrement/sass/tools'
,
you'll need to tell runSass
how to handle that. That will require writing a
custom importer
and passing it into the configuration for runSass
:
const path = require('path');
const { pathToFileURL } = require('url');
const sassTrue = require('sass-true');
const importers = [
{
findFileUrl(url) {
if (!url.startsWith('~')) {
return null;
}
return new URL(
pathToFileURL(path.resolve('node_modules', url.substring(1))),
);
},
},
];
const sassFile = path.join(__dirname, 'test.scss');
sassTrue.runSass({ describe, it }, sassFile, { importers });