jsenvassert
A powerful assertion library focused on providing clear, informative, and visual feedback for JavaScript tests.
equal() is my favorite assertion. If the only available assertion in every test suite was equal(), almost every test suite in the world would be better for it.
— Eric Elliot in Rethinking Unit Test Assertion
Simple Yet Powerful
import { assert } from "@jsenv/assert";
assert({
actual: {
foo: true,
},
expect: {
foo: false,
},
});
There is 200+ examples in ./tests/
Features
Color-Coded Diffs
Error messages use colors with specific meanings to make differences clear:
| Color | Meaning |
|---|---|
| grey | same in actual and expect |
| red | different from expect |
| green | different from actual |
| yellow | exists only in actual / exists only in expect |
JavaScript-Aware Comparisons
The library understands JavaScript types and provides meaningful differences:
assert({
actual: 149600000,
expect: 1464301,
});
Special handling extends to URLs, dates, HTTP headers, and more.
Beautiful Multiline String Diffs
assert({
actual: {
foo: `Hello,
my name is Benjamin
and my brother is joe`,
},
expect: {
foo: `Hello,
my name is Ben
and my brother is joe`,
},
});
Smart Formatting for Readability
Long diffs remain readable:
assert({
actual: "http://example_that_is_quite_long.com/dir/file.txt",
expect: "http://example_that_is_quite_long.com/dir/file.css",
});
Clear Nested Object Comparisons
For deeply nested objects, the message focuses on the important differences:
assert({
actual: {
the: {
nesting: {
is: {
very: {
deep: {
in: {
this: {
one: {
foo: {
a: true,
tata: { test: true, bar: { a: "1" } },
},
},
},
},
},
},
},
},
},
},
expect: {
the: {
nesting: {
is: {
very: {
deep: {
in: {
this: {
one: {
foo: false,
},
},
},
},
},
},
},
},
},
});
Custom assertions
assert({
actual: 50,
expect: assert.between(100, 200),
});
Advanced JavaScript Features
@jsenv/assert handles complex JavaScript concepts:
- Circular references
- Prototype differences example
- Object integrity differences (
Object.freeze,Object.sealandObject.preventExtensions) example - Property descriptor differences example
- Symbol differences example
Installation
Node.js
npm i --save-dev @jsenv/assertimport { assert } from "@jsenv/assert";
assert({
actual: true,
expect: false,
});Browser
Using NPM
npm i --save-dev @jsenv/assert<script type="module">
import { assert } from "@jsenv/assert";
assert({
actual: true,
expect: false,
});
</script>Using CDN
<script type="module">
import { assert } from "https://unpkg.com/@jsenv/assert@latest";
assert({
actual: true,
expect: false,
});
</script>