From fede4e4fb24b85a46e9b44a9dc521c3287a7a301 Mon Sep 17 00:00:00 2001
From: Bryan Ingle <bryaningle@gmail.com>
Date: Thu, 27 Jan 2022 11:43:30 -0700
Subject: [PATCH] Add "Null" and "Undefined" specifications (and tests)

---
 .releases/4.18.0.md                        |  3 +-
 specifications/Null.js                     | 31 +++++++++++++++++++++
 specifications/Undefined.js                | 31 +++++++++++++++++++++
 test/specs/specifications/NullSpec.js      | 31 +++++++++++++++++++++
 test/specs/specifications/UndefinedSpec.js | 32 ++++++++++++++++++++++
 5 files changed, 127 insertions(+), 1 deletion(-)
 create mode 100644 specifications/Null.js
 create mode 100644 specifications/Undefined.js
 create mode 100644 test/specs/specifications/NullSpec.js
 create mode 100644 test/specs/specifications/UndefinedSpec.js

diff --git a/.releases/4.18.0.md b/.releases/4.18.0.md
index c8eb04d..1bd63e3 100644
--- a/.releases/4.18.0.md
+++ b/.releases/4.18.0.md
@@ -1,4 +1,5 @@
 **New Features**
 
 * Added a `Changes` specification.
-* Added an `Exists` specification.
\ No newline at end of file
+* Added a `Null` specification.
+* Added an `Undefined` specification.
\ No newline at end of file
diff --git a/specifications/Null.js b/specifications/Null.js
new file mode 100644
index 0000000..b9637bf
--- /dev/null
+++ b/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;
+})();
+
+
diff --git a/specifications/Undefined.js b/specifications/Undefined.js
new file mode 100644
index 0000000..6775812
--- /dev/null
+++ b/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;
+})();
+
+
diff --git a/test/specs/specifications/NullSpec.js b/test/specs/specifications/NullSpec.js
new file mode 100644
index 0000000..573d56c
--- /dev/null
+++ b/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);
+	});
+});
\ No newline at end of file
diff --git a/test/specs/specifications/UndefinedSpec.js b/test/specs/specifications/UndefinedSpec.js
new file mode 100644
index 0000000..d64dc3c
--- /dev/null
+++ b/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);
+	});
+});
\ No newline at end of file