diff --git a/test/mjsunit/es6/array-concat-arraylike-string-length.js b/test/mjsunit/es6/array-concat-arraylike-string-length.js
index 471dcb99eb..0263113019 100644
--- a/test/mjsunit/es6/array-concat-arraylike-string-length.js
+++ b/test/mjsunit/es6/array-concat-arraylike-string-length.js
@@ -12,6 +12,6 @@ var obj = {
 obj[Symbol.isConcatSpreadable] = true;
 var obj2 = { length: 3, "0": "0", "1": "1", "2": "2" };
 var arr = ["X", "Y", "Z"];
-assertEquals([void 0, "A", void 0, "B", void 0, "C",
+assertEquals([, "A", , "B", , "C",
              { "length": 3, "0": "0", "1": "1", "2": "2" },
              "X", "Y", "Z"], Array.prototype.concat.call(obj, obj2, arr));
diff --git a/test/mjsunit/es6/array-concat-arraylike.js b/test/mjsunit/es6/array-concat-arraylike.js
index 0ad3eb5293..371d0f6e21 100644
--- a/test/mjsunit/es6/array-concat-arraylike.js
+++ b/test/mjsunit/es6/array-concat-arraylike.js
@@ -12,6 +12,6 @@ var obj = {
 obj[Symbol.isConcatSpreadable] = true;
 var obj2 = { length: 3, "0": "0", "1": "1", "2": "2" };
 var arr = ["X", "Y", "Z"];
-assertEquals([void 0, "A", void 0, "B", void 0, "C",
+assertEquals([, "A", , "B", , "C",
              { "length": 3, "0": "0", "1": "1", "2": "2" },
              "X", "Y", "Z"], Array.prototype.concat.call(obj, obj2, arr));
diff --git a/test/mjsunit/es6/array-concat-holey-array.js b/test/mjsunit/es6/array-concat-holey-array.js
index 31c2ba1bd9..19989b42c7 100644
--- a/test/mjsunit/es6/array-concat-holey-array.js
+++ b/test/mjsunit/es6/array-concat-holey-array.js
@@ -7,5 +7,5 @@ var arr = [];
 arr[4] = "Item 4";
 arr[8] = "Item 8";
 var arr2 = [".", "!", "?"];
-assertEquals([void 0, void 0, void 0, void 0, "Item 4", void 0, void 0,
-              void 0, "Item 8", ".", "!", "?"], arr.concat(arr2));
+assertEquals(
+    [, , , , 'Item 4', , , , 'Item 8', '.', '!', '?'], arr.concat(arr2));
diff --git a/test/mjsunit/es6/array-concat-sloppy-arguments-holey.js b/test/mjsunit/es6/array-concat-sloppy-arguments-holey.js
index ac160fc1f3..711a450bdf 100644
--- a/test/mjsunit/es6/array-concat-sloppy-arguments-holey.js
+++ b/test/mjsunit/es6/array-concat-sloppy-arguments-holey.js
@@ -5,4 +5,4 @@
 var args = (function(a) { return arguments; })(1,2,3);
 delete args[1];
 args[Symbol.isConcatSpreadable] = true;
-assertEquals([1, void 0, 3, 1, void 0, 3], [].concat(args, args));
+assertEquals([1, , 3, 1, , 3], [].concat(args, args));
diff --git a/test/mjsunit/es6/array-concat-sloppy-arguments-with-dupes.js b/test/mjsunit/es6/array-concat-sloppy-arguments-with-dupes.js
index 4634cac705..fed914780a 100644
--- a/test/mjsunit/es6/array-concat-sloppy-arguments-with-dupes.js
+++ b/test/mjsunit/es6/array-concat-sloppy-arguments-with-dupes.js
@@ -7,4 +7,4 @@ args[Symbol.isConcatSpreadable] = true;
 assertEquals([1, 2, 3, 1, 2, 3], [].concat(args, args));
 
 Object.defineProperty(args, "length", { value: 6 });
-assertEquals([1, 2, 3, void 0, void 0, void 0], [].concat(args));
+assertEquals([1, 2, 3, , , ,], [].concat(args));
diff --git a/test/mjsunit/es6/array-concat-sloppy-arguments.js b/test/mjsunit/es6/array-concat-sloppy-arguments.js
index b77833f885..346d07e870 100644
--- a/test/mjsunit/es6/array-concat-sloppy-arguments.js
+++ b/test/mjsunit/es6/array-concat-sloppy-arguments.js
@@ -7,4 +7,4 @@ args[Symbol.isConcatSpreadable] = true;
 assertEquals([1, 2, 3, 1, 2, 3], [].concat(args, args));
 
 Object.defineProperty(args, "length", { value: 6 });
-assertEquals([1, 2, 3, void 0, void 0, void 0], [].concat(args));
+assertEquals([1, 2, 3, , ,, ], [].concat(args));
diff --git a/test/mjsunit/es6/array-concat-spreadable-function.js b/test/mjsunit/es6/array-concat-spreadable-function.js
index 9b64fc63aa..1fea92b7e2 100644
--- a/test/mjsunit/es6/array-concat-spreadable-function.js
+++ b/test/mjsunit/es6/array-concat-spreadable-function.js
@@ -14,7 +14,7 @@ assertEquals([1, 2, 3], [].concat(fn));
 
 Function.prototype[Symbol.isConcatSpreadable] = true;
 // Functions may be concat-spreadable
-assertEquals([void 0, void 0, void 0], [].concat(function(a,b,c) {}));
+assertEquals(new Array(3), [].concat(function(a,b,c) {}));
 Function.prototype[0] = 1;
 Function.prototype[1] = 2;
 Function.prototype[2] = 3;
diff --git a/test/mjsunit/es6/array-concat-spreadable-nonarraylike-proxy.js b/test/mjsunit/es6/array-concat-spreadable-nonarraylike-proxy.js
index ecbe4488d7..f32c0e1d9b 100644
--- a/test/mjsunit/es6/array-concat-spreadable-nonarraylike-proxy.js
+++ b/test/mjsunit/es6/array-concat-spreadable-nonarraylike-proxy.js
@@ -36,7 +36,7 @@ assertEquals(["get", target, "length", obj], log[1]);
 target.length = 3;
 
 log.length = 0;
-assertEquals(["a", "b", undefined], [].concat(obj));
+assertEquals(["a", "b", ,], [].concat(obj));
 assertEquals(7, log.length);
 for (var i in log) assertSame(target, log[i][1]);
 assertEquals(["get", target, Symbol.isConcatSpreadable, obj], log[0]);
@@ -48,7 +48,7 @@ assertEquals(["get", target, "1", obj], log[5]);
 assertEquals(["has", target, "2"], log[6]);
 
 log.length = 0;
-assertEquals(["a", "b", undefined], Array.prototype.concat.apply(obj));
+assertEquals(["a", "b", ,], Array.prototype.concat.apply(obj));
 assertEquals(7, log.length);
 for (var i in log) assertSame(target, log[i][1]);
 assertEquals(["get", target, Symbol.isConcatSpreadable, obj], log[0]);
diff --git a/test/mjsunit/es6/array-concat-spreadable-regexp.js b/test/mjsunit/es6/array-concat-spreadable-regexp.js
index 73a61e4d88..54b9372caf 100644
--- a/test/mjsunit/es6/array-concat-spreadable-regexp.js
+++ b/test/mjsunit/es6/array-concat-spreadable-regexp.js
@@ -16,7 +16,7 @@ assertEquals([1, 2, 3], [].concat(re));
 RegExp.prototype[Symbol.isConcatSpreadable] = true;
 RegExp.prototype.length = 3;
 
-assertEquals([void 0, void 0, void 0], [].concat(/abc/));
+assertEquals(new Array(3), [].concat(/abc/));
 RegExp.prototype[0] = 1;
 RegExp.prototype[1] = 2;
 RegExp.prototype[2] = 3;
diff --git a/test/mjsunit/es6/array-concat-spreadable-sparse-object.js b/test/mjsunit/es6/array-concat-spreadable-sparse-object.js
index c10b002403..5227e7d6b7 100644
--- a/test/mjsunit/es6/array-concat-spreadable-sparse-object.js
+++ b/test/mjsunit/es6/array-concat-spreadable-sparse-object.js
@@ -5,7 +5,7 @@
 "use strict";
 var obj = { length: 5 };
 obj[Symbol.isConcatSpreadable] = true;
-assertEquals([void 0, void 0, void 0, void 0, void 0], [].concat(obj));
+assertEquals(new Array(5), [].concat(obj));
 
 obj.length = 4000;
 assertEquals(new Array(4000), [].concat(obj));
diff --git a/test/mjsunit/es6/array-concat-strict-arguments.js b/test/mjsunit/es6/array-concat-strict-arguments.js
index 4180a94a2e..106883168c 100644
--- a/test/mjsunit/es6/array-concat-strict-arguments.js
+++ b/test/mjsunit/es6/array-concat-strict-arguments.js
@@ -7,4 +7,4 @@ args[Symbol.isConcatSpreadable] = true;
 assertEquals([1, 2, 3, 1, 2, 3], [].concat(args, args));
 
 Object.defineProperty(args, "length", { value: 6 });
-assertEquals([1, 2, 3, void 0, void 0, void 0], [].concat(args));
+assertEquals([1, 2, 3, , , ,], [].concat(args));
diff --git a/test/mjsunit/es6/array-spread-holey.js b/test/mjsunit/es6/array-spread-holey.js
index 7d95e51b29..bea58e4952 100644
--- a/test/mjsunit/es6/array-spread-holey.js
+++ b/test/mjsunit/es6/array-spread-holey.js
@@ -6,7 +6,7 @@
 
 var a = [, 2];
 
-assertEquals([, 2], [...a]);
+assertEquals([undefined, 2], [...a]);
 assertTrue([...a].hasOwnProperty(0));
 assertTrue([2, ...a].hasOwnProperty(1));
 
diff --git a/test/mjsunit/harmony/array-prototype-groupby.js b/test/mjsunit/harmony/array-prototype-groupby.js
index cd6496f944..fdabfe831e 100644
--- a/test/mjsunit/harmony/array-prototype-groupby.js
+++ b/test/mjsunit/harmony/array-prototype-groupby.js
@@ -142,7 +142,7 @@ var group = () => {
 }
 
 assertEquals(group(), [
-  ['undefined', [,]],
+  ['undefined', [undefined]],
 ]);
 
 array.__proto__.push(6);
diff --git a/test/mjsunit/harmony/array-prototype-groupbytomap.js b/test/mjsunit/harmony/array-prototype-groupbytomap.js
index 265e84181f..84ac13cf8a 100644
--- a/test/mjsunit/harmony/array-prototype-groupbytomap.js
+++ b/test/mjsunit/harmony/array-prototype-groupbytomap.js
@@ -147,7 +147,7 @@ var groupToMap = () => {
 }
 
 assertEquals(groupToMap(), [
-  [undefined, [,]],
+  [undefined, [undefined]],
 ]);
 array.__proto__.push(6);
 assertEquals(groupToMap(), [
diff --git a/test/mjsunit/harmony/array-to-sorted.js b/test/mjsunit/harmony/array-to-sorted.js
index e5ea813fb8..d32523a7fa 100644
--- a/test/mjsunit/harmony/array-to-sorted.js
+++ b/test/mjsunit/harmony/array-to-sorted.js
@@ -7,32 +7,39 @@
 assertEquals(1, Array.prototype.toSorted.length);
 assertEquals("toSorted", Array.prototype.toSorted.name);
 
-function TerribleCopy(input) {
+function TerribleCopy(input, fillHoles) {
   let copy;
   if (Array.isArray(input)) {
-    copy = [...input];
+    copy = new Array(input.length);
   } else {
     copy = { length: input.length };
-    for (let i = 0; i < input.length; i++) {
+  }
+  for (let i = 0; i < input.length; ++i) {
+    if (i in input) {
       copy[i] = input[i];
+    } else if (fillHoles) {
+      copy[i] = undefined;
     }
   }
   return copy;
 }
 
 function AssertToSortedAndSortSameResult(input, ...args) {
-  const orig = TerribleCopy(input);
+  const orig = TerribleCopy(input, false);
   const s = Array.prototype.toSorted.apply(input, args);
-  const copy = TerribleCopy(input);
+  const copy = TerribleCopy(input, true);
   Array.prototype.sort.apply(copy, args);
 
   // The in-place sorted version should be pairwise equal to the toSorted,
-  // modulo being an actual Array if the input is generic.
+  // modulo being an actual Array if the input is generic, and holes should
+  // be filled with undefined.
   if (Array.isArray(input)) {
     assertEquals(copy, s);
   } else {
     assertEquals(copy.length, s.length);
     for (let i = 0; i < copy.length; i++) {
+      assertTrue(i in copy);
+      assertTrue(i in s);
       assertEquals(copy[i], s[i]);
     }
   }
diff --git a/test/mjsunit/keyed-store-array-literal.js b/test/mjsunit/keyed-store-array-literal.js
index 000385b9d3..d2bf5beec6 100644
--- a/test/mjsunit/keyed-store-array-literal.js
+++ b/test/mjsunit/keyed-store-array-literal.js
@@ -8,7 +8,7 @@
 function f1() {
   const x = [,];
   x[1] = 42;
-  assertEquals([undefined, 42], x);
+  assertEquals([, 42], x);
 }
 
 %PrepareFunctionForOptimization(f1);
diff --git a/test/mjsunit/mjsunit-assert-equals.js b/test/mjsunit/mjsunit-assert-equals.js
index 08154827d5..4f686df9fe 100644
--- a/test/mjsunit/mjsunit-assert-equals.js
+++ b/test/mjsunit/mjsunit-assert-equals.js
@@ -70,6 +70,8 @@ function testAssertEquals(a, b) {
   testAssertEquals(new Array(1), new Array(1));
   testAssertNotEquals(new Array(1), new Array(2));
   testAssertEquals([,,], new Array(2));
+  // The difference between empty and undefined is not ignored.
+  testAssertNotEquals([undefined], new Array(1));
 })();
 
 (function TestAssertEqualsArraysNested() {
@@ -80,9 +82,7 @@ function testAssertEquals(a, b) {
 })();
 
 (function TestAssertEqualsArrayProperties() {
-  // Difference between empty and undefined is ignored by the assert
-  // implementation as well as additional properties.
-  testAssertEquals([undefined], new Array(1));
+  // Array properties are ignored.
   let arrWithProp = new Array();
   arrWithProp.myProperty = 'Additional property';
   testAssertEquals([], arrWithProp);
diff --git a/test/mjsunit/mjsunit.js b/test/mjsunit/mjsunit.js
index 43298b3b7d..a8cba41f8c 100644
--- a/test/mjsunit/mjsunit.js
+++ b/test/mjsunit/mjsunit.js
@@ -432,6 +432,7 @@ var prettyPrinted;
         return false;
       }
       for (var i = 0; i < a.length; i++) {
+        if ((i in a) !== (i in b)) return false;
         if (!deepEquals(a[i], b[i])) return false;
       }
       return true;
diff --git a/test/mjsunit/regress/regress-165637.js b/test/mjsunit/regress/regress-165637.js
index 2a7fc4421f..60ca8d2e69 100644
--- a/test/mjsunit/regress/regress-165637.js
+++ b/test/mjsunit/regress/regress-165637.js
@@ -4,7 +4,7 @@
 
 // Make sure that packed and unpacked array slices are still properly handled
 var holey_array = [1, 2, 3, 4, 5,,,,,,];
-assertEquals([undefined], holey_array.slice(6, 7));
+assertEquals(new Array(1), holey_array.slice(6, 7));
 assertEquals(undefined, holey_array.slice(6, 7)[0]);
 assertEquals([], holey_array.slice(2, 1));
 assertEquals(3, holey_array.slice(2, 3)[0]);
diff --git a/test/mjsunit/regress/regress-804177.js b/test/mjsunit/regress/regress-804177.js
index b100480599..685bed1c03 100644
--- a/test/mjsunit/regress/regress-804177.js
+++ b/test/mjsunit/regress/regress-804177.js
@@ -25,7 +25,7 @@
   }
   b = Array.of.call(f,1,2);
   b[4] = 1;
-  assertEquals(b, [1, 2, undefined, undefined, 1]);
+  assertEquals(b, [1, 2, , , 1]);
 })();
 
 // Tests that using Array.of with a constructor returning an object with an
diff --git a/test/mjsunit/typedarray-resizablearraybuffer-array-methods.js b/test/mjsunit/typedarray-resizablearraybuffer-array-methods.js
index ee42e097b9..f6c31297ca 100644
--- a/test/mjsunit/typedarray-resizablearraybuffer-array-methods.js
+++ b/test/mjsunit/typedarray-resizablearraybuffer-array-methods.js
@@ -373,8 +373,7 @@ d8.file.execute('test/mjsunit/typedarray-helpers.js');
     const fixedLength = new ctor(rab, 0, 4);
     const evil = { valueOf: () => { rab.resize(2 * ctor.BYTES_PER_ELEMENT);
                                     return 0; }};
-    assertEquals([undefined, undefined, undefined, undefined],
-                sliceHelper(fixedLength, evil));
+    assertEquals(new Array(4), sliceHelper(fixedLength, evil));
     assertEquals(2 * ctor.BYTES_PER_ELEMENT, rab.byteLength);
   }
   for (let ctor of ctors) {
@@ -401,8 +400,7 @@ d8.file.execute('test/mjsunit/typedarray-helpers.js');
     const fixedLength = new ctor(rab, 0, 4);
     const evil = { valueOf: () => { %ArrayBufferDetach(rab);
                                     return 0; }};
-    assertEquals([undefined, undefined, undefined, undefined],
-                 sliceHelper(fixedLength, evil));
+    assertEquals(new Array(4), sliceHelper(fixedLength, evil));
     assertEquals(0, rab.byteLength);
   }
   for (let ctor of ctors) {
@@ -414,8 +412,9 @@ d8.file.execute('test/mjsunit/typedarray-helpers.js');
     }
     const evil = { valueOf: () => { %ArrayBufferDetach(rab);
                                     return 0; }};
-    assertEquals([undefined, undefined, undefined, undefined],
-                ToNumbers(sliceHelper(lengthTracking, evil)));
+    assertEquals(
+        [undefined, undefined, undefined, undefined],
+        ToNumbers(sliceHelper(lengthTracking, evil)));
     assertEquals(0, rab.byteLength);
   }
 })();