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- # assert
-
- [![Build Status](https://travis-ci.org/browserify/commonjs-assert.svg?branch=master)](https://travis-ci.org/browserify/commonjs-assert)
-
- This module is used for writing unit tests for your applications, you can access it with `require('assert')`.
-
- 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.
- 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.
-
- A `strict` and a `legacy` mode exist, while it is recommended to only use `strict mode`.
-
- ## Strict mode
-
- 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()`.
-
- It can be accessed using:
-
- ```js
- const assert = require('assert').strict;
- ```
-
- ## Legacy mode
-
- > Deprecated: Use strict mode instead.
-
- When accessing `assert` directly instead of using the `strict` property, the
- [Abstract Equality Comparison](https://tc39.github.io/ecma262/#sec-abstract-equality-comparison) will be used for any function without a
- "strict" in its name (e.g. `assert.deepEqual()`).
-
- It can be accessed using:
-
- ```js
- const assert = require('assert');
- ```
-
- It is recommended to use the `strict mode` instead as the Abstract Equality Comparison can often have surprising results. Especially
- in case of `assert.deepEqual()` as the used comparison rules there are very lax.
-
- E.g.
-
- ```js
- // WARNING: This does not throw an AssertionError!
- assert.deepEqual(/a/gi, new Date());
- ```
-
-
- ## assert.fail(actual, expected, message, operator)
- Throws an exception that displays the values for actual and expected separated by the provided operator.
-
- ## assert(value, message), assert.ok(value, [message])
- Tests if value is truthy, it is equivalent to assert.equal(true, !!value, message);
-
- ## assert.equal(actual, expected, [message])
- Tests shallow, coercive equality with the equal comparison operator ( == ).
-
- ## assert.notEqual(actual, expected, [message])
- Tests shallow, coercive non-equality with the not equal comparison operator ( != ).
-
- ## assert.deepEqual(actual, expected, [message])
- Tests for deep equality.
-
- ## assert.deepStrictEqual(actual, expected, [message])
- Tests for deep equality, as determined by the strict equality operator ( === )
-
- ## assert.notDeepEqual(actual, expected, [message])
- Tests for any deep inequality.
-
- ## assert.strictEqual(actual, expected, [message])
- Tests strict equality, as determined by the strict equality operator ( === )
-
- ## assert.notStrictEqual(actual, expected, [message])
- Tests strict non-equality, as determined by the strict not equal operator ( !== )
-
- ## assert.throws(block, [error], [message])
- Expects block to throw an error. error can be constructor, regexp or validation function.
-
- Validate instanceof using constructor:
-
- ```javascript
- assert.throws(function() { throw new Error("Wrong value"); }, Error);
- ```
-
- Validate error message using RegExp:
-
- ```javascript
- assert.throws(function() { throw new Error("Wrong value"); }, /value/);
- ```
-
- Custom error validation:
-
- ```javascript
- assert.throws(function() {
- throw new Error("Wrong value");
- }, function(err) {
- if ( (err instanceof Error) && /value/.test(err) ) {
- return true;
- }
- }, "unexpected error");
- ```
-
- ## assert.doesNotThrow(block, [message])
- Expects block not to throw an error, see assert.throws for details.
-
- ## assert.ifError(value)
- 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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