Add "Null" and "Undefined" specifications (and tests)

.releases/4.18.0.md

@@ -1,4 +1,5 @@
 **New Features**
 
 * Added a `Changes` specification.
-* Added an `Exists` specification.
+* Added a `Null` specification.
+* Added an `Undefined` specification.

specifications/Null.js

@@ -0,0 +1,31 @@
+const is = require('./../lang/is');
+
+const Specification = require('./Specification');
+
+module.exports = (() => {
+	'use strict';
+
+	/**
+	 * A {@link Specification} that passes when a data item is a null value.
+	 *
+	 * @public
+	 * @extends {Specification}
+	 */
+	class Null extends Specification {
+		constructor() {
+			super();
+		}
+
+		_evaluate(data) {
+			return is.null(data);
+		}
+
+		toString() {
+			return '[Null]';
+		}
+	}
+
+	return Null;
+})();
+
+

specifications/Undefined.js

@@ -0,0 +1,31 @@
+const is = require('./../lang/is');
+
+const Specification = require('./Specification');
+
+module.exports = (() => {
+	'use strict';
+
+	/**
+	 * A {@link Specification} that passes when a data item is an undefined value.
+	 *
+	 * @public
+	 * @extends {Specification}
+	 */
+	class Undefined extends Specification {
+		constructor() {
+			super();
+		}
+
+		_evaluate(data) {
+			return is.undefined(data);
+		}
+
+		toString() {
+			return '[Undefined]';
+		}
+	}
+
+	return Undefined;
+})();
+
+

test/specs/specifications/NullSpec.js

@@ -0,0 +1,31 @@
+const Null = require('./../../../specifications/Null');
+
+describe('When a Null specification is constructed', () => {
+	'use strict';
+
+	let specification;
+
+	beforeEach(() => {
+		specification = new Null();
+	});
+
+	it('should pass a null value', () => {
+		expect(specification.evaluate(null)).toEqual(true);
+	});
+
+	it('should not pass an implicit undefined value', () => {
+		expect(specification.evaluate()).toEqual(false);
+	});
+
+	it('should not pass an explicit undefined value', () => {
+		expect(specification.evaluate(undefined)).toEqual(false);
+	});
+
+	it('should not pass a zero value', () => {
+		expect(specification.evaluate(0)).toEqual(false);
+	});
+
+	it('should not pass an empty-length string value', () => {
+		expect(specification.evaluate('')).toEqual(false);
+	});
+});

test/specs/specifications/UndefinedSpec.js

@@ -0,0 +1,32 @@
+const Undefined = require('./../../../specifications/Undefined');
+
+describe('When a Undefined specification is constructed', () => {
+	'use strict';
+
+	let specification;
+
+	beforeEach(() => {
+		specification = new Undefined();
+	});
+
+	it('should not pass a null value', () => {
+		expect(specification.evaluate(null)).toEqual(false);
+	});
+
+	it('should pass an implicit undefined value', () => {
+		expect(specification.evaluate()).toEqual(true);
+	});
+
+	it('should pass an explicit undefined value', () => {
+		expect(specification.evaluate(undefined)).toEqual(true);
+	});
+
+
+	it('should not pass a zero value', () => {
+		expect(specification.evaluate(0)).toEqual(false);
+	});
+
+	it('should not pass an empty-length string value', () => {
+		expect(specification.evaluate('')).toEqual(false);
+	});
+});