Use Object.is when testing for equality where the === operator was previously used

README.md

@@ -95,7 +95,7 @@ expect(null, 'to be falsy');
 expect(undefined, 'to be falsy');
 ```
 
-**be**: asserts `===` equality
+**be**: asserts equality using `Object.is`/the [SameValue](http://people.mozilla.org/~jorendorff/es6-draft.html#sec-samevalue) algorithm
 
 ```js
 expect(obj, 'to be', obj);
@@ -117,6 +117,13 @@ expect(false, 'to be defined');
 expect({}, 'to be defined');
 ```
 
+The SameValue/`Object.is` algorithm has some subtle differences compared to the `===` operator, which makes it more suitable for an assertion lib:
+
+```js
+expect(NaN, 'to be', NaN);
+expect(-0, 'not to be', 0);
+```
+
 **equal**: asserts deep equality that works with objects
 
 ```js

documentation/assertions/any/to-be.md

@@ -1,4 +1,4 @@
-Asserts `===` equality.
+Asserts equality using `Object.is`/the [SameValue](http://people.mozilla.org/~jorendorff/es6-draft.html#sec-samevalue) algorithm.
 
 ```javascript
 var obj = {};
@@ -9,6 +9,15 @@ expect(undefined, 'to be', obj.foo);
 expect(true, 'to be', !false);
 ```
 
+The SameValue/`Object.is` algorithm has some subtle differences compared to the `===` operator, which makes it more suitable for an assertion lib:
+
+<!-- evaluate -->
+```javascript
+expect(NaN, 'to be', NaN);
+expect(-0, 'not to be', 0);
+```
+<!-- /evaluate -->
+
 In case of a failing expectation you get the following output:
 
 ```javascript

lib/Unexpected.js

@@ -12,9 +12,7 @@ var anyType = {
     identify: function () {
         return true;
     },
-    equal: function (a, b) {
-        return a === b;
-    },
+    equal: utils.objectIs,
     inspect: function (value, depth, output) {
         return output.text(value);
     },

lib/assertions.js

@@ -1,4 +1,5 @@
 var utils = require('./utils');
+var objectIs = utils.objectIs;
 var isRegExp = utils.isRegExp;
 var isArray = utils.isArray;
 var extend = utils.extend;
@@ -13,7 +14,7 @@ module.exports = function (expect) {
     });
 
     expect.addAssertion('[not] to be', function (expect, subject, value) {
-        expect(subject === value, '[not] to be truthy');
+        expect(objectIs(subject, value), '[not] to be truthy');
     });
 
     expect.addAssertion('string', '[not] to be', function (expect, subject, value) {

lib/types.js

@@ -862,7 +862,12 @@ module.exports = function (expect) {
             return typeof value === 'number';
         },
         inspect: function (value, depth, output) {
-            output.jsNumber(value);
+            if (value === 0 && 1 / value === -Infinity) {
+                value = '-0';
+            } else {
+                value = String(value);
+            }
+            output.jsNumber(String(value));
         }
     });
 

lib/utils.js

@@ -8,6 +8,17 @@ var errorMethodBlacklist = ['message', 'line', 'sourceId', 'sourceURL', 'stack',
 var specialCharRegexp = /([\x00-\x09\x0B-\x1F\x7F-\x9F\xAD\u0378\u0379\u037F-\u0383\u038B\u038D\u03A2\u0528-\u0530\u0557\u0558\u0560\u0588\u058B-\u058E\u0590\u05C8-\u05CF\u05EB-\u05EF\u05F5-\u0605\u061C\u061D\u06DD\u070E\u070F\u074B\u074C\u07B2-\u07BF\u07FB-\u07FF\u082E\u082F\u083F\u085C\u085D\u085F-\u089F\u08A1\u08AD-\u08E3\u08FF\u0978\u0980\u0984\u098D\u098E\u0991\u0992\u09A9\u09B1\u09B3-\u09B5\u09BA\u09BB\u09C5\u09C6\u09C9\u09CA\u09CF-\u09D6\u09D8-\u09DB\u09DE\u09E4\u09E5\u09FC-\u0A00\u0A04\u0A0B-\u0A0E\u0A11\u0A12\u0A29\u0A31\u0A34\u0A37\u0A3A\u0A3B\u0A3D\u0A43-\u0A46\u0A49\u0A4A\u0A4E-\u0A50\u0A52-\u0A58\u0A5D\u0A5F-\u0A65\u0A76-\u0A80\u0A84\u0A8E\u0A92\u0AA9\u0AB1\u0AB4\u0ABA\u0ABB\u0AC6\u0ACA\u0ACE\u0ACF\u0AD1-\u0ADF\u0AE4\u0AE5\u0AF2-\u0B00\u0B04\u0B0D\u0B0E\u0B11\u0B12\u0B29\u0B31\u0B34\u0B3A\u0B3B\u0B45\u0B46\u0B49\u0B4A\u0B4E-\u0B55\u0B58-\u0B5B\u0B5E\u0B64\u0B65\u0B78-\u0B81\u0B84\u0B8B-\u0B8D\u0B91\u0B96-\u0B98\u0B9B\u0B9D\u0BA0-\u0BA2\u0BA5-\u0BA7\u0BAB-\u0BAD\u0BBA-\u0BBD\u0BC3-\u0BC5\u0BC9\u0BCE\u0BCF\u0BD1-\u0BD6\u0BD8-\u0BE5\u0BFB-\u0C00\u0C04\u0C0D\u0C11\u0C29\u0C34\u0C3A-\u0C3C\u0C45\u0C49\u0C4E-\u0C54\u0C57\u0C5A-\u0C5F\u0C64\u0C65\u0C70-\u0C77\u0C80\u0C81\u0C84\u0C8D\u0C91\u0CA9\u0CB4\u0CBA\u0CBB\u0CC5\u0CC9\u0CCE-\u0CD4\u0CD7-\u0CDD\u0CDF\u0CE4\u0CE5\u0CF0\u0CF3-\u0D01\u0D04\u0D0D\u0D11\u0D3B\u0D3C\u0D45\u0D49\u0D4F-\u0D56\u0D58-\u0D5F\u0D64\u0D65\u0D76-\u0D78\u0D80\u0D81\u0D84\u0D97-\u0D99\u0DB2\u0DBC\u0DBE\u0DBF\u0DC7-\u0DC9\u0DCB-\u0DCE\u0DD5\u0DD7\u0DE0-\u0DF1\u0DF5-\u0E00\u0E3B-\u0E3E\u0E5C-\u0E80\u0E83\u0E85\u0E86\u0E89\u0E8B\u0E8C\u0E8E-\u0E93\u0E98\u0EA0\u0EA4\u0EA6\u0EA8\u0EA9\u0EAC\u0EBA\u0EBE\u0EBF\u0EC5\u0EC7\u0ECE\u0ECF\u0EDA\u0EDB\u0EE0-\u0EFF\u0F48\u0F6D-\u0F70\u0F98\u0FBD\u0FCD\u0FDB-\u0FFF\u10C6\u10C8-\u10CC\u10CE\u10CF\u1249\u124E\u124F\u1257\u1259\u125E\u125F\u1289\u128E\u128F\u12B1\u12B6\u12B7\u12BF\u12C1\u12C6\u12C7\u12D7\u1311\u1316\u1317\u135B\u135C\u137D-\u137F\u139A-\u139F\u13F5-\u13FF\u169D-\u169F\u16F1-\u16FF\u170D\u1715-\u171F\u1737-\u173F\u1754-\u175F\u176D\u1771\u1774-\u177F\u17DE\u17DF\u17EA-\u17EF\u17FA-\u17FF\u180F\u181A-\u181F\u1878-\u187F\u18AB-\u18AF\u18F6-\u18FF\u191D-\u191F\u192C-\u192F\u193C-\u193F\u1941-\u1943\u196E\u196F\u1975-\u197F\u19AC-\u19AF\u19CA-\u19CF\u19DB-\u19DD\u1A1C\u1A1D\u1A5F\u1A7D\u1A7E\u1A8A-\u1A8F\u1A9A-\u1A9F\u1AAE-\u1AFF\u1B4C-\u1B4F\u1B7D-\u1B7F\u1BF4-\u1BFB\u1C38-\u1C3A\u1C4A-\u1C4C\u1C80-\u1CBF\u1CC8-\u1CCF\u1CF7-\u1CFF\u1DE7-\u1DFB\u1F16\u1F17\u1F1E\u1F1F\u1F46\u1F47\u1F4E\u1F4F\u1F58\u1F5A\u1F5C\u1F5E\u1F7E\u1F7F\u1FB5\u1FC5\u1FD4\u1FD5\u1FDC\u1FF0\u1FF1\u1FF5\u1FFF\u200B-\u200F\u202A-\u202E\u2060-\u206F\u2072\u2073\u208F\u209D-\u209F\u20BA-\u20CF\u20F1-\u20FF\u218A-\u218F\u23F4-\u23FF\u2427-\u243F\u244B-\u245F\u2700\u2B4D-\u2B4F\u2B5A-\u2BFF\u2C2F\u2C5F\u2CF4-\u2CF8\u2D26\u2D28-\u2D2C\u2D2E\u2D2F\u2D68-\u2D6E\u2D71-\u2D7E\u2D97-\u2D9F\u2DA7\u2DAF\u2DB7\u2DBF\u2DC7\u2DCF\u2DD7\u2DDF\u2E3C-\u2E7F\u2E9A\u2EF4-\u2EFF\u2FD6-\u2FEF\u2FFC-\u2FFF\u3040\u3097\u3098\u3100-\u3104\u312E-\u3130\u318F\u31BB-\u31BF\u31E4-\u31EF\u321F\u32FF\u4DB6-\u4DBF\u9FCD-\u9FFF\uA48D-\uA48F\uA4C7-\uA4CF\uA62C-\uA63F\uA698-\uA69E\uA6F8-\uA6FF\uA78F\uA794-\uA79F\uA7AB-\uA7F7\uA82C-\uA82F\uA83A-\uA83F\uA878-\uA87F\uA8C5-\uA8CD\uA8DA-\uA8DF\uA8FC-\uA8FF\uA954-\uA95E\uA97D-\uA97F\uA9CE\uA9DA-\uA9DD\uA9E0-\uA9FF\uAA37-\uAA3F\uAA4E\uAA4F\uAA5A\uAA5B\uAA7C-\uAA7F\uAAC3-\uAADA\uAAF7-\uAB00\uAB07\uAB08\uAB0F\uAB10\uAB17-\uAB1F\uAB27\uAB2F-\uABBF\uABEE\uABEF\uABFA-\uABFF\uD7A4-\uD7AF\uD7C7-\uD7CA\uD7FC-\uF8FF\uFA6E\uFA6F\uFADA-\uFAFF\uFB07-\uFB12\uFB18-\uFB1C\uFB37\uFB3D\uFB3F\uFB42\uFB45\uFBC2-\uFBD2\uFD40-\uFD4F\uFD90\uFD91\uFDC8-\uFDEF\uFDFE\uFDFF\uFE1A-\uFE1F\uFE27-\uFE2F\uFE53\uFE67\uFE6C-\uFE6F\uFE75\uFEFD-\uFF00\uFFBF-\uFFC1\uFFC8\uFFC9\uFFD0\uFFD1\uFFD8\uFFD9\uFFDD-\uFFDF\uFFE7\uFFEF-\uFFFB\uFFFE\uFFFF])/g;
 
 var utils = module.exports = {
+    objectIs: Object.is || function (a, b) {
+        // Polyfill from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
+        if (a === 0 && b === 0) {
+            return 1 / a === 1 / b;
+        }
+        if (a !== a) {
+            return b !== b;
+        }
+        return a === b;
+    },
+
     // https://gist.github.com/1044128/
     getOuterHTML: function (element) {
         // jshint browser:true

test/unexpected.spec.js

@@ -182,6 +182,22 @@ describe('unexpected', function () {
             expect('', 'to be defined');
         });
 
+        it('NaN as equal to NaN', function () {
+            expect(NaN, 'to be', NaN);
+        });
+
+        it('considers negative zero not to be zero', function () {
+            expect(-0, 'not to be', 0);
+        });
+
+        it('considers negative zero to be itself', function () {
+            expect(-0, 'to be', -0);
+        });
+
+        it('considers zero to be itself', function () {
+            expect(0, 'to be', 0);
+        });
+
         it.skipIf(typeof Buffer === 'undefined', 'asserts === equality for Buffers', function () {
             var buffer = new Buffer([0x45, 0x59]);
             expect(buffer, 'to be', buffer);
@@ -330,6 +346,22 @@ describe('unexpected', function () {
             expect(new Error('foo'), 'to equal', new Error('foo'));
         });
 
+        it('treats NaN as equal to NaN', function () {
+            expect(NaN, 'to equal', NaN);
+        });
+
+        it('treats negative zero and zero as unequal', function () {
+            expect(-0, 'not to equal', 0);
+        });
+
+        it('treats negative zero as equal to itself', function () {
+            expect(-0, 'to equal', -0);
+        });
+
+        it('treats zero as equal to itself', function () {
+            expect(0, 'to equal', 0);
+        });
+
         it('treats an arguments object as different from an array', function () {
             (function () {
                 expect(arguments, 'not to equal', ['foo', 'bar', 'baz']);
@@ -3147,6 +3179,14 @@ describe('unexpected', function () {
                 expect(NaN, 'to inspect as', 'NaN');
             });
 
+            it('renders zero correctly', function () {
+                expect(0, 'to inspect as', '0');
+            });
+
+            it('renders negative zero correctly', function () {
+                expect(-0, 'to inspect as', '-0');
+            });
+
             it('renders Infinity correctly', function () {
                 expect(Infinity, 'to inspect as', 'Infinity');
             });