### Introduction

**code** was created as a direct rewrite of the powerful [**chai**](http://chaijs.com) assertions
library. This virtual fork was created for a few reasons. First, **chai** mixed usage of methods and
properties creates a problematic environment in which it is too easy to forget a method `()` and result
in an assertion that is never executed (and therefore passes incorrectly). This observation was noted by
the [**must**](https://github.com/moll/js-must) author.

The second reason is that similar to [**lab**](https://github.com/hapijs/lab), our test runner, we wanted
an assertion library that is small, simple, and intuitive - without plugins, extensions, or the overhead
of having to support testing in the browser. **code** provides much of the same functionality in about
300 lines of code that are trivial to read in a few minutes.

And last, we wanted to experiment with some new features that allow deeper integration between the test
runner and assertions library. The first of which are two methods exported (and used by **lab**) for getting
the total assertions count (which is a measure of the tests comprehensiveness), and by verifying that every
assertion created (e.g. every `expect()` call) is also executed. This will alert when a statement like
`expect(5).to.be.a.string` is not allowed to remain unnoticed (and fail to throw due to the missing `()`).

Like **lab**, the goal is to keep this module small and simple. If you need extensibility or other
functionality, we recommend looking at the many other excellent assertions libraries available.

### Example

```js
const Code = require('@hapi/code');
const expect = Code.expect;

expect(true).to.be.a.boolean().and.to.not.equal(false);
expect('this string').to.only.include(['this', 'string']);
```

### Grammar

**code** supports usage of connecting words to make assertions more readable. The inclusion of these
grammar elements has no impact over the assertion outcome and are used for human readability only.
Every method or property of the assertion object returned by `expect()` returns `this` which allows
chaining addition assertions or grammar words.

The supported words are:
- `a`
- `an`
- `and`
- `at`
- `be`
- `have`
- `in`
- `to`

```js
const Code = require('code');
const expect = Code.expect;

expect(10).to.be.above(5);
expect('abc').to.be.a.string();
expect([1, 2]).to.be.an.array();
expect(20).to.be.at.least(20);
expect('abc').to.have.length(3);
expect('abc').to.be.a.string().and.contain(['a', 'b']);
expect(6).to.be.in.range(5, 6);
```

### Flags

The following words toggle a status flag for the current assertion:
- `not` - inverses the expected result of any assertion.
- `once` - requires that inclusion matches appear only once in the provided value. Used by `include()`.
- `only` - requires that only the provided elements appear in the provided value. Used by `include()`.
- `part` - allows a partial match when asserting inclusion. Used by `include()`. Defaults to `false`.
- `shallow` - performs a comparison using strict equality (`===`). Code defaults to deep comparison. Used by `equal()` and `include()`.

```js
const Code = require('code');
const expect = Code.expect;

expect(10).to.not.be.above(20);
expect([1, 2, 3]).to.shallow.include(3);
expect([1, 1, 2]).to.only.include([1, 2]);
expect([1, 2]).to.once.include([1, 2]);
expect([1, 2, 3]).to.part.include([1, 4]);
```

Note that including the same flag twice toggles the last value set. This is especially important when
chaining multiple assertions in a single statement (e.g. when using the `and` grammar word).

### `expect(value, [prefix])`

Generates an assertion object where:
- `value` - the reference value on which to apply the assertion rules.
- `prefix` - an optional string used as an error message prefix.

```js
const Code = require('code');
const expect = Code.expect;

expect(10, 'Age').to.be.above(5);
```

#### Types

Asserts that the reference value is of a certain type.

##### `arguments()`

Asserts that the reference value is an `arguments` object.

```js
const Code = require('code');
const expect = Code.expect;
const func = function () { return arguments; };
expect(func()).to.be.arguments();
```

##### `array()`

Asserts that the reference value is an `Array`.

```js
const Code = require('code');
const expect = Code.expect;

expect([1, 2]).to.be.an.array();
```

##### `boolean()`

Asserts that the reference value is a boolean.

```js
const Code = require('code');
const expect = Code.expect;

expect(true).to.be.a.boolean();
```

##### `buffer()`

Asserts that the reference value is a `Buffer`.

```js
const Code = require('code');
const expect = Code.expect;

expect(new Buffer('')).to.be.a.buffer();
```

##### `date()`

Asserts that the reference value is a `Date`.

```js
const Code = require('code');
const expect = Code.expect;

expect(new Date()).to.be.a.date();
```

##### `error([type], [message])`

Asserts that the reference value is an error. You can provide optional requirements where:
- `type` - the `instanceof` value of the error.
- `message` a string or regular expression matching the error `message` property. Note that a string
  must provide a full match.

```js
const Code = require('code');
const expect = Code.expect;

const err = new Error('Oops an error occured.');
expect(err).to.be.an.error();
expect(err).to.be.an.error(Error);
expect(err).to.be.an.error('Oops an error occured.');
expect(err).to.be.an.error(Error, /occured/);
```

##### `function()`

Asserts that the reference value is a `function`.

```js
const Code = require('code');
const expect = Code.expect;

expect(function () {}).to.be.a.function();
```

##### `number()`

Asserts that the reference value is a `number`.

```js
const Code = require('code');
const expect = Code.expect;

expect(123).to.be.a.number();
```

##### `regexp()`

Asserts that the reference value is an `RegExp`.

```js
const Code = require('code');
const expect = Code.expect;

expect(/abc/).to.be.a.regexp();
```

##### `string()`

Asserts that the reference value is a string.

```js
const Code = require('code');
const expect = Code.expect;

expect('abc').to.be.a.string();
```

##### `object()`

Asserts that the reference value is an object (excluding array, buffer, or other native objects).

```js
const Code = require('code');
const expect = Code.expect;

expect({ a: '1' }).to.be.an.object();
```

#### Values

Asserts that the reference value is equal to a predefined value.

##### `true()`

Asserts that the reference value is true.

```js
const Code = require('code');
const expect = Code.expect;

expect(true).to.be.true();
```

##### `false()`

Asserts that the reference value is false.

```js
const Code = require('code');
const expect = Code.expect;

expect(false).to.be.false();
```

##### `null()`

Asserts that the reference value is null.

```js
const Code = require('code');
const expect = Code.expect;

expect(null).to.be.null();
```

##### `undefined()`

Asserts that the reference value is undefined.

```js
const Code = require('code');
const expect = Code.expect;

expect(undefined).to.be.undefined();
```

##### `NaN()`

Asserts that the reference value is `NaN`.

```js
const Code = require('code');
const expect = Code.expect;

expect(NaN).to.be.NaN();
```

#### `include(values)`

Aliases: `includes()`, `contain()`, `contains()`

See also: [`Hoek.contain()`](https://github.com/hapijs/hoek/blob/master/API.md#containref-values-options)

Asserts that the reference value (a string, array, or object) includes the provided values where:
- `values` - a single or array of values. If the reference value is a string, the values must be strings.
  If the reference value is an array, the values can be any array member. If the reference value is an object, the values can be key names, or a single object
  with key-value pairs to match.

```js
const Code = require('code');
const expect = Code.expect;

expect('abc').to.include('ab');
expect('abc').to.only.include('abc');
expect('aaa').to.only.include('a');
expect('abc').to.once.include('b');
expect('abc').to.include(['a', 'c']);
expect('abc').to.part.include(['a', 'd']);

expect([1, 2, 3]).to.include(1);
expect([{ a: 1 }]).to.include({ a: 1 });
expect([1, 2, 3]).to.include([1, 2]);
expect([{ a: 1 }]).to.include([{ a: 1 }]);
expect([1, 1, 2]).to.only.include([1, 2]);
expect([1, 2]).to.once.include([1, 2]);
expect([1, 2, 3]).to.part.include([1, 4]);
expect([[1], [2]]).to.include([[1]]);

expect({ a: 1, b: 2, c: 3 }).to.include('a');
expect({ a: 1, b: 2, c: 3 }).to.include(['a', 'c']);
expect({ a: 1, b: 2, c: 3 }).to.only.include(['a', 'b', 'c']);
expect({ a: 1, b: 2, c: 3 }).to.include({ a: 1 });
expect({ a: 1, b: 2, c: 3 }).to.include({ a: 1, c: 3 });
expect({ a: 1, b: 2, c: 3 }).to.part.include({ a: 1, d: 4 });
expect({ a: 1, b: 2, c: 3 }).to.only.include({ a: 1, b: 2, c: 3 });
expect({ a: [1], b: [2], c: [3] }).to.include({ a: [1], c: [3] });
```

#### `startWith(value)`

Aliases: `startsWith()`,

Asserts that the reference value (a string) starts with the provided value where:
- `value` - a string.

Note that this assertion is case sensitive.

```js
const Code = require('code');
const expect = Code.expect;

expect('https://example.org/secure').to.startWith('https://');
```

#### `endWith(value)`

Aliases: `endsWith()`,

Asserts that the reference value (a string) ends with the provided value where:
- `value` - a string.

Note that this assertion is case sensitive.

```js
const Code = require('code');
const expect = Code.expect;

expect('http://example.org/relative').to.endWith('/relative');
```

#### `exist()`

Aliases: `exists`

Asserts that the reference value exists (not `null` or `undefined`).

```js
const Code = require('code');
const expect = Code.expect;

expect(4).to.exist();
expect(null).to.not.exist();
```


#### `empty()`

Asserts that the reference value has a `length` property equal to zero or an object with no keys.

```js
const Code = require('code');
const expect = Code.expect;

expect('abc').to.be.empty();
```

#### `length(size)`

Asserts that the reference value has a `length` property matching the provided size or an object with the
specified number of keys where:
- `size` - the required size.

```js
const Code = require('code');
const expect = Code.expect;

expect('abcd').to.have.length(4);
```

#### `equal(value[, options])`

Aliases: `equals()`

Asserts that the reference value equals the provided value where:
- `value` - the value to compare to.
- `options` - optional object specifying comparison options. This is ignored on `shallow` comparisons.

```js
const Code = require('code');
const expect = Code.expect;

expect(5).to.equal(5);
expect({ a: 1 }).to.equal({ a: 1 });
```

Deep comparisons (the default) are performed using
[`Hoek.deepEqual()`](https://github.com/hapijs/hoek/blob/master/API.md#deepequalb-a-options). The
optional `options` argument is passed directly to `Hoek.deepEqual()`. An example
deep comparison which ignores object prototypes is shown below.

```js
const Code = require('code');
const expect = Code.expect;

expect(Object.create(null)).to.equal({}, { prototype: false });
```

Strict equality can be checked using the `shallow` modifier. This yields the same output as a `===` check.

```js
const Code = require('code');
const expect = Code.expect;

expect(5).to.shallow.equal(5);
expect({ a: 1 }).to.shallow.equal({ a: 1 }); // fails as they are not the same reference
```

#### `above(value)`

Aliases: `greaterThan()`

Asserts that the reference value is greater than (`>`) the provided value where:
- `value` - the value to compare to.

```js
const Code = require('code');
const expect = Code.expect;

expect(10).to.be.above(5);
```

#### `least(value)`

Aliases: `min()`

Asserts that the reference value is at least (`>=`) the provided value where:
- `value` - the value to compare to.

```js
const Code = require('code');
const expect = Code.expect;

expect(10).to.be.at.least(10);
```

#### `below(value)`

Aliases: `lessThan()`

Asserts that the reference value is less than (`<`) the provided value where:
- `value` - the value to compare to.

```js
const Code = require('code');
const expect = Code.expect;

expect(10).to.be.below(20);
```

#### `most(value)`

Aliases: `max()`

Asserts that the reference value is at most (`<=`) the provided value where:
- `value` - the value to compare to.

```js
const Code = require('code');
const expect = Code.expect;

expect(10).to.be.at.most(10);
```

#### `within(from, to)`

Aliases: `range()`

Asserts that the reference value is within (`from <= value <= to`) the provided values where:
- `from` - the start of the range (inclusive).
- `to` - the end of the range (inclusive).

```js
const Code = require('code');
const expect = Code.expect;

expect(10).to.be.within(10, 20);
expect(20).to.be.within(10, 20);
```

#### `between(from, to)`

Asserts that the reference value is between but not equal (`from < value < to`) the provided values where:
- `from` - the start of the range (exclusive).
- `to` - the end of the range (exclusive).

```js
const Code = require('code');
const expect = Code.expect;

expect(15).to.be.between(10, 20);
```

#### `about(value, delta)`

Asserts that the reference value is about the provided value within a delta margin of difference where:
- `value` - the value to compare to.
- `delta` - the allowed margin of difference.

```js
const Code = require('code');
const expect = Code.expect;

expect(10).to.be.about(9, 1);
```

#### `instanceof(type)`

Aliases: `instanceOf()`

Asserts that the reference value has the provided `instanceof` value where:
- `type` - the type value to match.

```js
const Code = require('code');
const expect = Code.expect;

expect(new Date()).to.be.an.instanceof(Date);
```

#### `match(regex)`

Aliases: `matches()`

Asserts that the reference value's `toString()` representation matches the provided regular
expression where:
- `regex` - the regular expression to match.

```js
const Code = require('code');
const expect = Code.expect;

expect('a5').to.match(/\w\d/);
expect(["abc", "def"]).to.match(/^[\w\d,]*$/);
expect(1).to.match(/^\d$/);
```

#### `satisfy(validator)`

Aliases: `satisfies()`

Asserts that the reference value satisfies the provided validator function where:
- `validator` - a function with the signature `function(value)` with return value `true` or `false`. The
  reference value is passed as the only argument to the `validator` function and the assertion passes if
  the return value is `true`.

```js
const Code = require('code');
const expect = Code.expect;

expect('x').to.satisfy(function (value) { return value === 'x'; });
```

#### `throw([type], [message])`

Aliases: `throws`

Asserts that the function reference value throws an exception when called. The provided reference function
is invoked within a `try`-`catch` block and any error throws is caught and compared to the provided optional
requirements where:
- `type` - the `instanceof` value of the thrown object.
- `message` a string or regular expression matching the thrown error `message` property. Note that a string
  must provide a full match.

```js
const NodeUtil = require('util');
const Code = require('code');
const expect = Code.expect;

const CustomError = function (message) {

    Error.call(this, message);
};

NodeUtil.inherit(CustomError, Error)

const throws = function () {

    throw new CustomError('Oh no!');
};

expect(throws).to.throw(CustomError, 'Oh no!');
```

#### `await reject([type], [message])`

Aliases: `rejects`

Asserts that the `Promise` reference value rejects with an exception when called. The provided reference
promise is resolved using an `await` statement within a `try`-`catch` block and any error throws is caught
and compared to the provided optional requirements where:
- `type` - the `instanceof` value of the rejected object.
- `message` a string or regular expression matching the rejected error `message` property. Note that a string
  must provide a full match.

Returns a promise resolving to the rejected error object.

```js
const NodeUtil = require('util');
const Code = require('code');
const expect = Code.expect;

const CustomError = function (message, code) {

    this.message = message;
    this.code = code;
};

NodeUtil.inherits(CustomError, Error);

const rejects = function () {

    return new Promise((resolve, reject) => reject(new CustomError('Oh no!', 123)));
};

const err = await expect(rejects()).to.reject(CustomError, 'Oh no!');
expect(err.code).to.equal(123);
```

### `fail(message)`

Makes the test fail with `message`.

```js
const Code = require('code');

Code.fail('This should not occur');
```

### `count()`

Returns the total number of assertions created using the `expect()` method.

```js
const Code = require('code');
const expect = Code.expect;

expect(5).to.not.be.a.string();
console.log(Code.count());		// -> 1
```

### `incomplete()`

Returns an array of the locations where incomplete assertions were declared or `null` if no incomplete assertions found.

```js
const Code = require('code');
const expect = Code.expect;

expect(5).to.not.be.a.string;
console.log(Code.incomplete());		// -> [ 'readme.js:667:1' ]
```

### `thrownAt([error])`

Returns the filename, line number, and column number of where the `error` was created. If no error is provided, the current location returned.

```js
const Code = require('code');

const error = new Error('oops');
Code.thrownAt(error);
```

### Settings

**code** can be configured using the module's `settings` object. The following
settings are supported:

#### `truncateMessages`

A Boolean value that, when `true`, causes long assertion error messages to be
truncated for readability. Setting this to `false` causes the entire message
to be displayed. Defaults to `true`.

```js
const Code = require('code');
const expect = Code.expect;
const foo = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12];

Code.settings.truncateMessages = false;
expect(foo).to.equal([]);
```

#### `comparePrototypes`

A Boolean value that, when `false`, ignores object prototypes when doing a deep comparison. Defaults to `false`.

```js
const Code = require('code');
const expect = Code.expect;
const foo = Object.create(null);

Code.settings.comparePrototypes = false;
expect(foo).to.equal({});

Code.settings.comparePrototypes = true;
expect(foo).to.equal({}); // fails
```