assert: fix _deepEqual and improve assert.md

doc/api/assert.md

@@ -43,13 +43,17 @@ changes:
 -->
 
 Tests for deep equality between the `actual` and `expected` parameters.
-Primitive values are compared with the equal comparison operator ( `==` ).
-
-Only enumerable "own" properties are considered. The `deepEqual()`
-implementation does not test object prototypes, attached symbols, or
-non-enumerable properties. This can lead to some potentially surprising
-results. For example, the following example does not throw an `AssertionError`
-because the properties on the [`Error`][] object are non-enumerable:
+Primitive values are compared with the [Abstract Equality Comparison][]
+( `==` ).
+
+Only [enumerable "own" properties][] are considered. The
+[`assert.deepEqual()`][] implementation does not test the
+[`[[Prototype]]`][prototype-spec] of objects, attached symbols, or
+non-enumerable properties — for such checks, consider using
+[assert.deepStrictEqual()][] instead. This can lead to some
+potentially surprising results. For example, the following example does not
+throw an `AssertionError` because the properties on the [`Error`][] object are
+not enumerable:
 
 ```js
 // WARNING: This does not throw an AssertionError!
@@ -113,17 +117,20 @@ changes:
     description: Handle non-`Uint8Array` typed arrays correctly.
 -->
 
-Generally identical to `assert.deepEqual()` with two exceptions. First,
-primitive values are compared using the strict equality operator ( `===` ).
-Second, object comparisons include a strict equality check of their prototypes.
+Generally identical to `assert.deepEqual()` with two exceptions:
+
+1. Primitive values are compared using the [Strict Equality Comparison][]
+  ( `===` ).
+2. [`[[Prototype]]`][prototype-spec] of objects are compared using
+  the [Strict Equality Comparison][] too.
 
 ```js
 const assert = require('assert');
 
-assert.deepEqual({a:1}, {a:'1'});
+assert.deepEqual({a: 1}, {a: '1'});
 // OK, because 1 == '1'
 
-assert.deepStrictEqual({a:1}, {a:'1'});
+assert.deepStrictEqual({a: 1}, {a: '1'});
 // AssertionError: { a: 1 } deepStrictEqual { a: '1' }
 // because 1 !== '1' using strict equality
 ```
@@ -200,7 +207,7 @@ added: v0.1.21
 -->
 
 Tests shallow, coercive equality between the `actual` and `expected` parameters
-using the equal comparison operator ( `==` ).
+using the [Abstract Equality Comparison][] ( `==` ).
 
 ```js
 const assert = require('assert');
@@ -330,7 +337,7 @@ the `message` parameter is undefined, a default error message is assigned.
 added: v0.1.21
 -->
 
-Tests shallow, coercive inequality with the not equal comparison operator
+Tests shallow, coercive inequality with the [Abstract Equality Comparison][]
 ( `!=` ).
 
 ```js
@@ -355,7 +362,7 @@ parameter is undefined, a default error message is assigned.
 added: v0.1.21
 -->
 
-Tests strict inequality as determined by the strict not equal operator
+Tests strict inequality as determined by the [Strict Equality Comparison][]
 ( `!==` ).
 
 ```js
@@ -407,7 +414,8 @@ assert.ok(false, 'it\'s false');
 added: v0.1.21
 -->
 
-Tests strict equality as determined by the strict equality operator ( `===` ).
+Tests strict equality as determined by the [Strict Equality Comparison][]
+( `===` ).
 
 ```js
 const assert = require('assert');
@@ -493,10 +501,43 @@ assert.throws(myFunction, 'missing foo', 'did not throw with expected message');
 assert.throws(myFunction, /missing foo/, 'did not throw with expected message');
 ```
 
+## Caveats
+
+For the following cases, consider using ES2015 [`Object.is()`][],
+which uses the [SameValueZero][] comparison.
+
+```js
+const a = 0;
+const b = -a;
+assert.notStrictEqual(a, b);
+// AssertionError: 0 !== -0
+// Strict Equality Comparison doesn't distinguish between -0 and +0...
+assert(!Object.is(a, b));
+// but Object.is() does!
+
+const str1 = "foo";
+const str2 = "foo";
+assert.strictEqual(str1 / 1, str2 / 1);
+// AssertionError: NaN === NaN
+// Strict Equality Comparison can't be used to check NaN...
+assert(Object.is(str1 / 1, str2 / 1));
+// but Object.is() can!
+```
+
+For more information, see
+[MDN's guide on equality comparisons and sameness][mdn-equality-guide].
+
 [`assert.deepEqual()`]: #assert_assert_deepequal_actual_expected_message
 [`assert.deepStrictEqual()`]: #assert_assert_deepstrictequal_actual_expected_message
 [`assert.ok()`]: #assert_assert_ok_value_message
 [`assert.throws()`]: #assert_assert_throws_block_error_message
 [`Error`]: errors.html#errors_class_error
 [`RegExp`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions
 [`TypeError`]: errors.html#errors_class_typeerror
+[Abstract Equality Comparison]: https://tc39.github.io/ecma262/#sec-abstract-equality-comparison
+[Strict Equality Comparison]: https://tc39.github.io/ecma262/#sec-strict-equality-comparison
+[`Object.is()`]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/is
+[SameValueZero]: https://tc39.github.io/ecma262/#sec-samevaluezero
+[prototype-spec]: https://tc39.github.io/ecma262/#sec-ordinary-object-internal-methods-and-internal-slots
+[mdn-equality-guide]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Equality_comparisons_and_sameness
+[enumerable "own" properties]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Enumerability_and_ownership_of_properties

lib/assert.js

@@ -23,8 +23,8 @@
 // UTILITY
 const compare = process.binding('buffer').compare;
 const util = require('util');
+const objectToString = require('internal/util').objectToString;
 const Buffer = require('buffer').Buffer;
-const pToString = (obj) => Object.prototype.toString.call(obj);
 
 // The assert module provides functions that throw
 // AssertionError's when particular conditions are not met. The
@@ -136,117 +136,177 @@ assert.deepStrictEqual = function deepStrictEqual(actual, expected, message) {
   }
 };
 
+function areSimilarRegExps(a, b) {
+  return a.source === b.source && a.flags === b.flags;
+}
+
+function areSimilarTypedArrays(a, b) {
+  return compare(Buffer.from(a.buffer,
+                             a.byteOffset,
+                             a.byteLength),
+                 Buffer.from(b.buffer,
+                             b.byteOffset,
+                             b.byteLength)) === 0;
+}
+
+function isNullOrNonObj(object) {
+  return object === null || typeof object !== 'object';
+}
+
+function isFloatTypedArrayTag(tag) {
+  return tag === '[object Float32Array]' || tag === '[object Float64Array]';
+}
+
+function isArguments(tag) {
+  return tag === '[object Arguments]';
+}
+
 function _deepEqual(actual, expected, strict, memos) {
   // All identical values are equivalent, as determined by ===.
   if (actual === expected) {
     return true;
+  }
 
-  // If both values are instances of buffers, equivalence is
-  // determined by comparing the values and ensuring the result
-  // === 0.
-  } else if (actual instanceof Buffer && expected instanceof Buffer) {
-    return compare(actual, expected) === 0;
-
-  // If the expected value is a Date object, the actual value is
-  // equivalent if it is also a Date object that refers to the same time.
-  } else if (util.isDate(actual) && util.isDate(expected)) {
-    return actual.getTime() === expected.getTime();
-
-  // If the expected value is a RegExp object, the actual value is
-  // equivalent if it is also a RegExp object with the same source and
-  // properties (`global`, `multiline`, `lastIndex`, `ignoreCase`).
-  } else if (util.isRegExp(actual) && util.isRegExp(expected)) {
-    return actual.source === expected.source &&
-           actual.global === expected.global &&
-           actual.multiline === expected.multiline &&
-           actual.lastIndex === expected.lastIndex &&
-           actual.ignoreCase === expected.ignoreCase;
-
-  // If both values are primitives, equivalence is determined by
-  // == or, if checking for strict equivalence, ===.
-  } else if ((actual === null || typeof actual !== 'object') &&
-             (expected === null || typeof expected !== 'object')) {
+  // For primitives / functions
+  // (determined by typeof value !== 'object'),
+  // or null, equivalence is determined by === or ==.
+  if (isNullOrNonObj(actual) && isNullOrNonObj(expected)) {
     return strict ? actual === expected : actual == expected;
+  }
 
-  // If both values are instances of typed arrays, wrap their underlying
-  // ArrayBuffers in a Buffer to increase performance.
-  // This optimization requires the arrays to have the same type as checked by
-  // Object.prototype.toString (pToString). Never perform binary
-  // comparisons for Float*Arrays, though, since +0 === -0 is true despite the
-  // two values' bit patterns not being identical.
-  } else if (ArrayBuffer.isView(actual) && ArrayBuffer.isView(expected) &&
-             pToString(actual) === pToString(expected) &&
-             !(actual instanceof Float32Array ||
-               actual instanceof Float64Array)) {
-    return compare(Buffer.from(actual.buffer,
-                               actual.byteOffset,
-                               actual.byteLength),
-                   Buffer.from(expected.buffer,
-                               expected.byteOffset,
-                               expected.byteLength)) === 0;
-
-  // For all other Object pairs, including Array objects, equivalence is
-  // determined by having the same number of owned properties (as verified
-  // with Object.prototype.hasOwnProperty.call), the same set of keys
-  // (although not necessarily the same order), equivalent values for every
-  // corresponding key, and an identical 'prototype' property. Note: this
-  // accounts for both named and indexed properties on Arrays.
-  } else {
-    memos = memos || {actual: [], expected: []};
+  // If they bypass the previous check, then at least
+  // one of them must be an non-null object.
+  // If the other one is null or undefined, they must not be equal.
+  if (actual === null || actual === undefined ||
+      expected === null || expected === undefined)
+    return false;
 
-    const actualIndex = memos.actual.indexOf(actual);
-    if (actualIndex !== -1) {
-      if (actualIndex === memos.expected.indexOf(expected)) {
-        return true;
-      }
+  // Notes: Type tags are historical [[Class]] properties that can be set by
+  // FunctionTemplate::SetClassName() in C++ or Symbol.toStringTag in JS
+  // and retrieved using Object.prototype.toString.call(obj) in JS
+  // See https://tc39.github.io/ecma262/#sec-object.prototype.tostring
+  // for a list of tags pre-defined in the spec.
+  // There are some unspecified tags in the wild too (e.g. typed array tags).
+  // Since tags can be altered, they only serve fast failures
+  const actualTag = objectToString(actual);
+  const expectedTag = objectToString(expected);
+
+  // Passing null or undefined to Object.getPrototypeOf() will throw
+  // so this must done after previous checks.
+  // For strict comparison, objects should have
+  // a) The same prototypes.
+  // b) The same built-in type tags
+  if (strict) {
+    if (Object.getPrototypeOf(actual) !== Object.getPrototypeOf(expected)) {
+      return false;
     }
+  }
 
-    memos.actual.push(actual);
-    memos.expected.push(expected);
+  // Do fast checks for builtin types.
+  // If they don't match, they must not be equal.
+  // If they match, return true for non-strict comparison.
+  // For strict comparison we need to exam further.
 
-    return objEquiv(actual, expected, strict, memos);
+  // If both values are Date objects,
+  // check if the time underneath are equal first.
+  if (util.isDate(actual) && util.isDate(expected)) {
+    if (actual.getTime() !== expected.getTime()) {
+      return false;
+    } else if (!strict) {
+      return true;  // Skip further checks for non-strict comparison.
+    }
   }
-}
 
-function isArguments(object) {
-  return Object.prototype.toString.call(object) === '[object Arguments]';
-}
+  // If both values are RegExp, check if they have
+  // the same source and flags first
+  if (util.isRegExp(actual) && util.isRegExp(expected)) {
+    if (!areSimilarRegExps(actual, expected)) {
+      return false;
+    } else if (!strict) {
+      return true;  // Skip further checks for non-strict comparison.
+    }
+  }
 
-function objEquiv(a, b, strict, actualVisitedObjects) {
-  if (a === null || a === undefined || b === null || b === undefined)
+  // Ensure reflexivity of deepEqual with `arguments` objects.
+  // See https://github.com/nodejs/node-v0.x-archive/pull/7178
+  if (isArguments(actualTag) !== isArguments(expectedTag)) {
     return false;
+  }
+
+  // Check typed arrays and buffers by comparing the content in their
+  // underlying ArrayBuffer. This optimization requires that it's
+  // reasonable to interpret their underlying memory in the same way,
+  // which is checked by comparing their type tags.
+  // (e.g. a Uint8Array and a Uint16Array with the same memory content
+  // could still be different because they will be interpreted differently)
+  // Never perform binary comparisons for Float*Arrays, though,
+  // since e.g. +0 === -0 is true despite the two values' bit patterns
+  // not being identical.
+  if (ArrayBuffer.isView(actual) && ArrayBuffer.isView(expected) &&
+      actualTag === expectedTag && !isFloatTypedArrayTag(actualTag)) {
+    if (!areSimilarTypedArrays(actual, expected)) {
+      return false;
+    } else if (!strict) {
+      return true;  // Skip further checks for non-strict comparison.
+    }
+
+    // Buffer.compare returns true, so actual.length === expected.length
+    // if they both only contain numeric keys, we don't need to exam further
+    if (Object.keys(actual).length === actual.length &&
+        Object.keys(expected).length === expected.length) {
+      return true;
+    }
+  }
+
+  // For all other Object pairs, including Array objects,
+  // equivalence is determined by having:
+  // a) The same number of owned enumerable properties
+  // b) The same set of keys/indexes (although not necessarily the same order)
+  // c) Equivalent values for every corresponding key/index
+  // Note: this accounts for both named and indexed properties on Arrays.
+
+  // Use memos to handle cycles.
+  memos = memos || { actual: [], expected: [] };
+  const actualIndex = memos.actual.indexOf(actual);
+  if (actualIndex !== -1) {
+    if (actualIndex === memos.expected.indexOf(expected)) {
+      return true;
+    }
+  }
+  memos.actual.push(actual);
+  memos.expected.push(expected);
 
-  // If one is a primitive, the other must be the same.
+  return objEquiv(actual, expected, strict, memos);
+}
+
+function objEquiv(a, b, strict, actualVisitedObjects) {
+  // If one of them is a primitive, the other must be the same.
   if (util.isPrimitive(a) || util.isPrimitive(b))
     return a === b;
-  if (strict && Object.getPrototypeOf(a) !== Object.getPrototypeOf(b))
-    return false;
-  const aIsArgs = isArguments(a);
-  const bIsArgs = isArguments(b);
-  if ((aIsArgs && !bIsArgs) || (!aIsArgs && bIsArgs))
-    return false;
-  const ka = Object.keys(a);
-  const kb = Object.keys(b);
+
+  const aKeys = Object.keys(a);
+  const bKeys = Object.keys(b);
   var key, i;
 
-  // The pair must have the same number of owned properties (keys
-  // incorporates hasOwnProperty).
-  if (ka.length !== kb.length)
+  // The pair must have the same number of owned properties
+  // (keys incorporates hasOwnProperty).
+  if (aKeys.length !== bKeys.length)
     return false;
 
   // The pair must have the same set of keys (although not
   // necessarily in the same order).
-  ka.sort();
-  kb.sort();
+  aKeys.sort();
+  bKeys.sort();
   // Cheap key test:
-  for (i = ka.length - 1; i >= 0; i--) {
-    if (ka[i] !== kb[i])
+  for (i = aKeys.length - 1; i >= 0; i--) {
+    if (aKeys[i] !== bKeys[i])
       return false;
   }
+
   // The pair must have equivalent values for every corresponding key.
   // Possibly expensive deep test:
-  for (i = ka.length - 1; i >= 0; i--) {
-    key = ka[i];
+  for (i = aKeys.length - 1; i >= 0; i--) {
+    key = aKeys[i];
     if (!_deepEqual(a[key], b[key], strict, actualVisitedObjects))
       return false;
   }
@@ -269,7 +329,6 @@ function notDeepStrictEqual(actual, expected, message) {
   }
 }
 
-
 // The strict equality assertion tests strict equality, as determined by ===.
 // assert.strictEqual(actual, expected, message_opt);
 
@@ -295,7 +354,7 @@ function expectedException(actual, expected) {
     return false;
   }
 
-  if (Object.prototype.toString.call(expected) === '[object RegExp]') {
+  if (objectToString(expected) === '[object RegExp]') {
     return expected.test(actual);
   }
 

test/parallel/test-assert-deep.js

@@ -0,0 +1,110 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+const util = require('util');
+
+// Template tag function turning an error message into a RegExp
+// for assert.throws()
+function re(literals, ...values) {
+  let result = literals[0];
+  for (const [i, value] of values.entries()) {
+    const str = util.inspect(value);
+    // Need to escape special characters.
+    result += str.replace(/[\\^$.*+?()[\]{}|=!<>:-]/g, '\\$&');
+    result += literals[i + 1];
+  }
+  return new RegExp(`^AssertionError: ${result}$`);
+}
+
+// The following deepEqual tests might seem very weird.
+// They just describe what it is now.
+// That is why we discourage using deepEqual in our own tests.
+
+// Turn off no-restricted-properties because we are testing deepEqual!
+/* eslint-disable no-restricted-properties */
+
+const arr = new Uint8Array([120, 121, 122, 10]);
+const buf = Buffer.from(arr);
+// They have different [[Prototype]]
+assert.throws(() => assert.deepStrictEqual(arr, buf));
+assert.doesNotThrow(() => assert.deepEqual(arr, buf));
+
+const buf2 = Buffer.from(arr);
+buf2.prop = 1;
+
+assert.throws(() => assert.deepStrictEqual(buf2, buf));
+assert.doesNotThrow(() => assert.deepEqual(buf2, buf));
+
+const arr2 = new Uint8Array([120, 121, 122, 10]);
+arr2.prop = 5;
+assert.throws(() => assert.deepStrictEqual(arr, arr2));
+assert.doesNotThrow(() => assert.deepEqual(arr, arr2));
+
+const date = new Date('2016');
+
+class MyDate extends Date {
+  constructor(...args) {
+    super(...args);
+    this[0] = '1';
+  }
+}
+
+const date2 = new MyDate('2016');
+
+// deepEqual returns true as long as the time are the same,
+// but deepStrictEqual checks own properties
+assert.doesNotThrow(() => assert.deepEqual(date, date2));
+assert.doesNotThrow(() => assert.deepEqual(date2, date));
+assert.throws(() => assert.deepStrictEqual(date, date2),
+              re`${date} deepStrictEqual ${date2}`);
+assert.throws(() => assert.deepStrictEqual(date2, date),
+              re`${date2} deepStrictEqual ${date}`);
+
+class MyRegExp extends RegExp {
+  constructor(...args) {
+    super(...args);
+    this[0] = '1';
+  }
+}
+
+const re1 = new RegExp('test');
+const re2 = new MyRegExp('test');
+
+// deepEqual returns true as long as the regexp-specific properties
+// are the same, but deepStrictEqual checks all properties
+assert.doesNotThrow(() => assert.deepEqual(re1, re2));
+assert.throws(() => assert.deepStrictEqual(re1, re2),
+              re`${re1} deepStrictEqual ${re2}`);
+
+// For these weird cases, deepEqual should pass (at least for now),
+// but deepStrictEqual should throw.
+const similar = new Set([
+  {0: '1'},  // Object
+  {0: 1},  // Object
+  new String('1'),  // Object
+  ['1'],  // Array
+  [1],  // Array
+  date2,  // Date with this[0] = '1'
+  re2,  // RegExp with this[0] = '1'
+  new Int8Array([1]), // Int8Array
+  new Uint8Array([1]), // Uint8Array
+  new Int16Array([1]), // Int16Array
+  new Uint16Array([1]), // Uint16Array
+  new Int32Array([1]), // Int32Array
+  new Uint32Array([1]), // Uint32Array
+  Buffer.from([1]),
+  // Arguments {'0': '1'} is not here
+  // See https://github.com/nodejs/node-v0.x-archive/pull/7178
+]);
+
+for (const a of similar) {
+  for (const b of similar) {
+    if (a !== b) {
+      assert.doesNotThrow(() => assert.deepEqual(a, b));
+      assert.throws(() => assert.deepStrictEqual(a, b),
+                    re`${a} deepStrictEqual ${b}`);
+    }
+  }
+}
+
+/* eslint-enable */

test/parallel/test-assert.js

@@ -62,7 +62,6 @@ assert.doesNotThrow(makeBlock(a.notStrictEqual, 2, '2'),
                     'notStrictEqual(2, \'2\')');
 
 // deepEqual joy!
-// 7.2
 assert.doesNotThrow(makeBlock(a.deepEqual, new Date(2000, 3, 14),
                               new Date(2000, 3, 14)),
                     'deepEqual(new Date(2000, 3, 14), new Date(2000, 3, 14))');
@@ -84,7 +83,6 @@ assert.doesNotThrow(makeBlock(
                     'notDeepEqual(new Date(), new Date(2000, 3, 14))'
 );
 
-// 7.3
 assert.doesNotThrow(makeBlock(a.deepEqual, /a/, /a/));
 assert.doesNotThrow(makeBlock(a.deepEqual, /a/g, /a/g));
 assert.doesNotThrow(makeBlock(a.deepEqual, /a/i, /a/i));
@@ -104,20 +102,16 @@ assert.throws(makeBlock(a.deepEqual, /a/igm, /a/im),
 {
   const re1 = /a/g;
   re1.lastIndex = 3;
-
-  assert.throws(makeBlock(a.deepEqual, re1, /a/g),
-                /^AssertionError: \/a\/g deepEqual \/a\/g$/);
+  assert.doesNotThrow(makeBlock(a.deepEqual, re1, /a/g),
+                      /^AssertionError: \/a\/g deepEqual \/a\/g$/);
 }
 
-
-// 7.4
 assert.doesNotThrow(makeBlock(a.deepEqual, 4, '4'), 'deepEqual(4, \'4\')');
 assert.doesNotThrow(makeBlock(a.deepEqual, true, 1), 'deepEqual(true, 1)');
 assert.throws(makeBlock(a.deepEqual, 4, '5'),
               a.AssertionError,
               'deepEqual( 4, \'5\')');
 
-// 7.5
 // having the same number of owned properties && the same set of keys
 assert.doesNotThrow(makeBlock(a.deepEqual, {a: 4}, {a: 4}));
 assert.doesNotThrow(makeBlock(a.deepEqual, {a: 4, b: '2'}, {a: 4, b: '2'}));
@@ -210,7 +204,6 @@ assert.doesNotThrow(
   'notDeepStrictEqual(new Date(), new Date(2000, 3, 14))'
 );
 
-// 7.3 - strict
 assert.doesNotThrow(makeBlock(a.deepStrictEqual, /a/, /a/));
 assert.doesNotThrow(makeBlock(a.deepStrictEqual, /a/g, /a/g));
 assert.doesNotThrow(makeBlock(a.deepStrictEqual, /a/i, /a/i));
@@ -240,10 +233,9 @@ assert.throws(
 {
   const re1 = /a/;
   re1.lastIndex = 3;
-  assert.throws(makeBlock(a.deepStrictEqual, re1, /a/));
+  assert.doesNotThrow(makeBlock(a.deepStrictEqual, re1, /a/));
 }
 
-// 7.4 - strict
 assert.throws(makeBlock(a.deepStrictEqual, 4, '4'),
               a.AssertionError,
               'deepStrictEqual(4, \'4\')');
@@ -256,7 +248,6 @@ assert.throws(makeBlock(a.deepStrictEqual, 4, '5'),
               a.AssertionError,
               'deepStrictEqual(4, \'5\')');
 
-// 7.5 - strict
 // having the same number of owned properties && the same set of keys
 assert.doesNotThrow(makeBlock(a.deepStrictEqual, {a: 4}, {a: 4}));
 assert.doesNotThrow(makeBlock(a.deepStrictEqual,

test/parallel/test-child-process-spawnsync-input.js

@@ -87,7 +87,8 @@ options = {
 ret = spawnSync('cat', [], options);
 
 checkSpawnSyncRet(ret);
-assert.deepStrictEqual(ret.stdout, options.input);
+// Wrap options.input because Uint8Array and Buffer have different prototypes.
+assert.deepStrictEqual(ret.stdout, Buffer.from(options.input));
 assert.deepStrictEqual(ret.stderr, Buffer.from(''));
 
 verifyBufOutput(spawnSync(process.execPath, args));

test/parallel/test-fs-read.js

@@ -18,11 +18,11 @@ function test(bufferAsync, bufferSync, expected) {
           common.mustCall((err, bytesRead) => {
             assert.ifError(err);
             assert.strictEqual(bytesRead, expected.length);
-            assert.deepStrictEqual(bufferAsync, Buffer.from(expected));
+            assert.deepStrictEqual(bufferAsync, expected);
           }));
 
   const r = fs.readSync(fd, bufferSync, 0, expected.length, 0);
-  assert.deepStrictEqual(bufferSync, Buffer.from(expected));
+  assert.deepStrictEqual(bufferSync, expected);
   assert.strictEqual(r, expected.length);
 }