106 lines
3.6 KiB
Markdown
106 lines
3.6 KiB
Markdown
# assert
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[](https://travis-ci.org/browserify/commonjs-assert)
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This module is used for writing unit tests for your applications, you can access it with `require('assert')`.
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It aims to be fully compatibe with the [node.js assert module](http://nodejs.org/api/assert.html), same API and same behavior, just adding support for web browsers.
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The API and code may contain traces of the [CommonJS Unit Testing 1.0 spec](http://wiki.commonjs.org/wiki/Unit_Testing/1.0) which they were based on, but both have evolved significantly since then.
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A `strict` and a `legacy` mode exist, while it is recommended to only use `strict mode`.
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## Strict mode
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When using the `strict mode`, any `assert` function will use the equality used in the strict function mode. So `assert.deepEqual()` will, for example, work the same as `assert.deepStrictEqual()`.
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It can be accessed using:
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```js
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const assert = require('assert').strict;
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```
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## Legacy mode
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> Deprecated: Use strict mode instead.
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When accessing `assert` directly instead of using the `strict` property, the
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[Abstract Equality Comparison](https://tc39.github.io/ecma262/#sec-abstract-equality-comparison) will be used for any function without a
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"strict" in its name (e.g. `assert.deepEqual()`).
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It can be accessed using:
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```js
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const assert = require('assert');
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```
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It is recommended to use the `strict mode` instead as the Abstract Equality Comparison can often have surprising results. Especially
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in case of `assert.deepEqual()` as the used comparison rules there are very lax.
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E.g.
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```js
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// WARNING: This does not throw an AssertionError!
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assert.deepEqual(/a/gi, new Date());
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```
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## assert.fail(actual, expected, message, operator)
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Throws an exception that displays the values for actual and expected separated by the provided operator.
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## assert(value, message), assert.ok(value, [message])
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Tests if value is truthy, it is equivalent to assert.equal(true, !!value, message);
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## assert.equal(actual, expected, [message])
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Tests shallow, coercive equality with the equal comparison operator ( == ).
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## assert.notEqual(actual, expected, [message])
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Tests shallow, coercive non-equality with the not equal comparison operator ( != ).
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## assert.deepEqual(actual, expected, [message])
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Tests for deep equality.
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## assert.deepStrictEqual(actual, expected, [message])
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Tests for deep equality, as determined by the strict equality operator ( === )
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## assert.notDeepEqual(actual, expected, [message])
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Tests for any deep inequality.
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## assert.strictEqual(actual, expected, [message])
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Tests strict equality, as determined by the strict equality operator ( === )
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## assert.notStrictEqual(actual, expected, [message])
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Tests strict non-equality, as determined by the strict not equal operator ( !== )
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## assert.throws(block, [error], [message])
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Expects block to throw an error. error can be constructor, regexp or validation function.
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Validate instanceof using constructor:
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```javascript
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assert.throws(function() { throw new Error("Wrong value"); }, Error);
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```
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Validate error message using RegExp:
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```javascript
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assert.throws(function() { throw new Error("Wrong value"); }, /value/);
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```
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Custom error validation:
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```javascript
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assert.throws(function() {
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throw new Error("Wrong value");
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}, function(err) {
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if ( (err instanceof Error) && /value/.test(err) ) {
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return true;
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}
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}, "unexpected error");
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```
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## assert.doesNotThrow(block, [message])
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Expects block not to throw an error, see assert.throws for details.
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## assert.ifError(value)
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Tests if value is not a false value, throws if it is a true value. Useful when testing the first argument, error in callbacks.
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