# Types Unexpected comes with a type system that is used to explain how different types are compared, diffed, inspected and is also used to limit the scope of assertions. The following types are provided by out of the box by Unexpected: `any`, `arguments`, `array`, `array-like`, `binaryArray`, `boolean`, `Buffer`, `date`, `Error`, `function`, `Int8Array`, `Int16Array`, `Int32Array`, `NaN`, `null`, `number`, `object`, `regexp`, `string`, `Uint8Array`, `Uint16Array`, `Uint32Array`, and `undefined`. ## expect.addType(typeDefinition) Unexpected can be extended with knowledge about new types by calling the `addType` method with a type definition. The type definition must implement the required parts of the following interface: Required members: * __name__: `String` - the name of the type. * __identify__: `boolean function(value)` - a function deciding if the type should be used for the given value. Note that your type has the option to take precedence over all the built-in types. Test subjects will be tested against the most recently defined type first, so `identify` functions should take care not to break with `undefined`, `null` and so on. Optional members: * __base__: `String` - the name of the base type. Defaults to `any`. * __equal__: `boolean function(a, b, equal)` - a function capable of comparing two values of this type for equality. If not specified it is inherited from the base type. * __inspect__: `function(value, depth, output, inspect)` - a function capable of inspecting a value of this type. If not specified it is inherited from the base type. * __diff__: `comparison function(actual, expected, output, diff, inspect)` - a function producing a comparison between two values of this type. If not specified it is inherited from the base type. ## Example Adding new types to the system is best explained by an example. Let's say we wanted to add first class support for a `Person` type: ```javascript function Person(name, age) { this.name = name; this.age = age; } ``` We start out by creating a basic type for handling `Person` instances. The name of the type should be `Person` and it should inherit from the built-in `object` type. Furthermore we add an `identify` method that will recognize `Person` instances. ```javascript expect.addType({ name: 'Person', base: 'object', identify: function (value) { return value instanceof Person; } }); ``` When you specify a base type, you inherit the optional members you didn't implement. In this case we inherited the methods `equal`, `inspect` and `diff` from the `object` type. Imagine that we make a failing expectation on a `Person` instance: ```javascript expect(new Person('John Doe', 42), 'to equal', new Person('Jane Doe', 24)); ``` ```output expected Person({ name: 'John Doe', age: 42 }) to equal Person({ name: 'Jane Doe', age: 24 }) Person({ name: 'John Doe', // should equal 'Jane Doe' // -John Doe // +Jane Doe age: 42 // should equal 24 }) ``` That is already quite helpful, but it would be even nicer if the stringification of `Person` instances could read as valid calls to the constructor. We can fix that by implementing an `inspect` method on the type. ```javascript#freshExpect:true expect.addType({ name: 'Person', base: 'object', identify: function (value) { return value instanceof Person; }, inspect: function (person, depth, output, inspect) { output.text('new Person(') .append(inspect(person.name, depth)) .text(', ') .append(inspect(person.age, depth)) .text(')'); } }); ``` Now we get the following output: ```javascript expect(new Person('John Doe', 42), 'to equal', new Person('Jane Doe', 24)); ``` ```output expected new Person('John Doe', 42) to equal new Person('Jane Doe', 24) Person({ name: 'John Doe', // should equal 'Jane Doe' // -John Doe // +Jane Doe age: 42 // should equal 24 }) ``` That is a bit better, let me explain how it works. The `inspect` method is called with the value to be inspected, the depth this type should be inspected with, an output the inspected value should be written to, and an inspect function that can be used to recursively inspect members. The output is an instance of [magicpen](https://github.com/unexpectedjs/magicpen) extended with a number of [styles](https://github.com/unexpectedjs/unexpected/blob/master/lib/styles.js). We write `new Person(` without styling, then we append the inspected `name`, write a `, `, inspect the `age` and finish with the closing parenthesis. When `inspect` is called without a depth parameter it defaults to `depth-1`. Values inspected with depth zero will be inspected as `...`. In this case we always want the name so we forward the same depth to the `inspect` function. Let's say we wanted `Person` instances only to be compared by name and not by age. Then we need to override the `equal` method: ```javascript#freshExpect:true expect.addType({ name: 'Person', base: 'object', identify: function (value) { return value instanceof Person; }, inspect: function (person, depth, output, inspect) { output.text('new Person(') .append(inspect(person.name, depth)) .text(', ') .append(inspect(person.age, depth)) .text(')'); }, equal: function (a, b, equal) { return a === b || equal(a.name, b.name); } }); ``` This will produce the same output as above, but that means the diff if wrong. It states that the age should be changed. We can fix that the following way: ```javascript#freshExpect:true expect.addType({ name: 'Person', base: 'object', identify: function (value) { return value instanceof Person; }, inspect: function (person, depth, output, inspect) { output.text('new Person(') .append(inspect(person.name, depth)) .text(', ') .append(inspect(person.age, depth)) .text(')'); }, equal: function (a, b, equal) { return a === b || equal(a.name, b.name); }, diff: function (actual, expected, output, diff, inspect) { return this.baseType.diff({name: actual.name}, {name: expected.name}, output); } }); ``` ```javascript expect(new Person('John Doe', 42), 'to equal', new Person('Jane Doe', 24)); ``` ```output expected new Person('John Doe', 42) to equal new Person('Jane Doe', 24) { name: 'John Doe' // should equal 'Jane Doe' // -John Doe // +Jane Doe } ``` The above `diff` method just calls the `diff` method on the base type with objects that only contain the name. The `object` diff will take care of all the hard work. We could also have called the `diff` function we got as an argument, but that will go off detecting the types of the parameters, therefore it is faster to call `diff` method on the base directly when you know it is the one you need. You could also do something really custom as seen below: ```javascript#freshExpect:true var inlineDiff = true; // used to change inlining in a later example expect.addType({ name: 'Person', base: 'object', identify: function (value) { return value instanceof Person; }, inspect: function (person, depth, output, inspect) { output.text('new Person(') .append(inspect(person.name, depth)) .text(', ') .append(inspect(person.age, depth)) .text(')'); }, equal: function (a, b, equal) { return a === b || equal(a.name, b.name); }, diff: function (actual, expected, output, diff, inspect) { var nameDiff = diff(actual.name, expected.name); output.text('new Person(') .nl() .indentLines(); if (nameDiff && nameDiff.inline) { output.append(nameDiff.diff); } else { output.i().append(inspect(actual.name)).text(',').sp() .annotationBlock(function () { this.error('should be ').append(inspect(expected.name)); if (nameDiff) { this.nl().append(nameDiff.diff); } }) .nl(); } output.i().append(inspect(actual.age)) .outdentLines() .nl() .text(')'); return { inline: inlineDiff, diff: output }; } }); ``` That would produce the following output. ```javascript expect(new Person('John Doe', 42), 'to equal', new Person('Jane Doe', 24)); ``` ```output expected new Person('John Doe', 42) to equal new Person('Jane Doe', 24) new Person( 'John Doe', // should be 'Jane Doe' // -John Doe // +Jane Doe 42 ) ``` This is a rather complicated example and I won't go though the details, but I would like to comment on the `inline` flag. When we diff objects against each other, the values of the keys will be diffed against each other. That means diffs are inserted into the containing structure. You can control this behavior using the `inline` flag. If the child diff is inline, it means that it will be appended directly into the parent; otherwise the diff will be inserted in an annotation block. The outputs below shows the contrast between setting the `Person` diff to inline or not. ```javascript inlineDiff = true; expect( {'John Doe': new Person('John Doe', 42), 'Jane Doe': new Person('Janie Doe', 24)}, 'to equal', {'John Doe': new Person('John Doe', 42), 'Jane Doe': new Person('Jane Doe', 24)} ); ``` ```output expected { 'John Doe': new Person('John Doe', 42), 'Jane Doe': new Person('Janie Doe', 24) } to equal { 'John Doe': new Person('John Doe', 42), 'Jane Doe': new Person('Jane Doe', 24) } { 'John Doe': new Person('John Doe', 42), 'Jane Doe': new Person( 'Janie Doe', // should be 'Jane Doe' // -Janie Doe // +Jane Doe 24 ) } ``` ```javascript inlineDiff = false; expect( {'John Doe': new Person('John Doe', 42), 'Jane Doe': new Person('Janie Doe', 24)}, 'to equal', {'John Doe': new Person('John Doe', 42), 'Jane Doe': new Person('Jane Doe', 24)} ); ``` ```output expected { 'John Doe': new Person('John Doe', 42), 'Jane Doe': new Person('Janie Doe', 24) } to equal { 'John Doe': new Person('John Doe', 42), 'Jane Doe': new Person('Jane Doe', 24) } { 'John Doe': new Person('John Doe', 42), 'Jane Doe': new Person('Janie Doe', 24) // should equal new Person('Jane Doe', 24) // new Person( // 'Janie Doe', // should be 'Jane Doe' // // -Janie Doe // // +Jane Doe // 24 // ) } ``` Now that we have implemented a type, we can start adding assertions to it. These assertions will only work on this type or types inheriting from the type. ```javascript expect.addAssertion('Person', 'to be above legal age', function (expect, subject) { expect(subject.age, 'to be greater than or equal to', 18); }); expect(new Person('Jane Doe', 24), 'to be above legal age'); ``` Because `Person` inherits from `object` you can use all assertion defined for `object` or any of its ancestors. Here is an example: ```javascript expect(new Person('Jane Doe', 24), 'to have keys', 'name', 'age'); expect(new Person('Jane Doe', 24), 'to satisfy', { name: expect.it('to be a string').and('not to be empty'), age: expect.it('to be a number').and('not to be negative') }); ``` The best resource for learning more about custom types is to look at how the predefined types are built: [lib/types.js](https://github.com/unexpectedjs/unexpected/blob/master/lib/types.js)