RAB: Integrate staging tests for the .reduceRight method (#4157)

* Import relevant files from #3888

* Removing parts in resizableArrayBufferUtils.js and adding it in includes,
while adjusting usage of CollectValuesAndResize and applying review changes
from PRs for previously tested methods.

* Added missing 'shrink' test for Array.prototype.reduceRight

test/built-ins/Array/prototype/reduceRight/resizable-buffer-grow-mid-iteration.js

@@ -0,0 +1,83 @@
+// Copyright 2023 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-array.prototype.reduceright
+description: >
+  Array.p.reduceRight behaves correctly on TypedArrays backed by resizable
+  buffers that are grown mid-iteration.
+includes: [compareArray.js, resizableArrayBufferUtils.js]
+features: [resizable-arraybuffer]
+---*/
+
+let values;
+let rab;
+let resizeAfter;
+let resizeTo;
+// Collects the view of the resizable array buffer rab into values, with an
+// iteration during which, after resizeAfter steps, rab is resized to length
+// resizeTo. To be called by a method of the view being collected.
+// Note that rab, values, resizeAfter, and resizeTo may need to be reset before
+// calling this.
+function ResizeBufferMidIteration(acc, n) {
+  return CollectValuesAndResize(n, values, rab, resizeAfter, resizeTo);
+}
+
+// Orig. array: [0, 2, 4, 6]
+//              [0, 2, 4, 6] << fixedLength
+//                    [4, 6] << fixedLengthWithOffset
+//              [0, 2, 4, 6, ...] << lengthTracking
+//                    [4, 6, ...] << lengthTrackingWithOffset
+
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const fixedLength = new ctor(rab, 0, 4);
+  resizeAfter = 2;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  Array.prototype.reduceRight.call(fixedLength, ResizeBufferMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const fixedLengthWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT, 2);
+  resizeAfter = 1;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  Array.prototype.reduceRight.call(fixedLengthWithOffset, ResizeBufferMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  resizeAfter = 2;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  Array.prototype.reduceRight.call(lengthTracking, ResizeBufferMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const lengthTrackingWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT);
+  resizeAfter = 1;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  Array.prototype.reduceRight.call(lengthTrackingWithOffset, ResizeBufferMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}

test/built-ins/Array/prototype/reduceRight/resizable-buffer-shrink-mid-iteration.js

@@ -0,0 +1,95 @@
+// Copyright 2023 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%array%.prototype.reduceright
+description: >
+  Array.p.reduceRight behaves correctly when the backing resizable buffer is
+  shrunk mid-iteration.
+includes: [compareArray.js, resizableArrayBufferUtils.js]
+features: [resizable-arraybuffer]
+---*/
+
+let values;
+let rab;
+let resizeAfter;
+let resizeTo;
+// Collects the view of the resizable array buffer rab into values, with an
+// iteration during which, after resizeAfter steps, rab is resized to length
+// resizeTo. To be called by a method of the view being collected.
+// Note that rab, values, resizeAfter, and resizeTo may need to be reset before
+// calling this.
+function ResizeMidIteration(acc, n) {
+  return CollectValuesAndResize(n, values, rab, resizeAfter, resizeTo);
+}
+
+// Orig. array: [0, 2, 4, 6]
+//              [0, 2, 4, 6] << fixedLength
+//                    [4, 6] << fixedLengthWithOffset
+//              [0, 2, 4, 6, ...] << lengthTracking
+//                    [4, 6, ...] << lengthTrackingWithOffset
+
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const fixedLength = new ctor(rab, 0, 4);
+  resizeAfter = 2;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  Array.prototype.reduceRight.call(fixedLength, ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const fixedLengthWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT, 2);
+  resizeAfter = 1;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  Array.prototype.reduceRight.call(fixedLengthWithOffset, ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  resizeAfter = 2;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  // Unaffected by the shrinking, since we've already iterated past the point.
+  Array.prototype.reduceRight.call(lengthTracking, ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  resizeAfter = 1;
+  resizeTo = 2 * ctor.BYTES_PER_ELEMENT;
+  Array.prototype.reduceRight.call(lengthTracking, ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const lengthTrackingWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT);
+  resizeAfter = 1;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  // Unaffected by the shrinking, since we've already iterated past the point.
+  Array.prototype.reduceRight.call(lengthTrackingWithOffset, ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}

test/built-ins/Array/prototype/reduceRight/resizable-buffer.js

@@ -0,0 +1,129 @@
+// Copyright 2023 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-array.prototype.reduceright
+description: >
+  Array.p.reduceRight behaves correctly on TypedArrays backed by resizable
+  buffers.
+includes: [compareArray.js, resizableArrayBufferUtils.js]
+features: [resizable-arraybuffer]
+---*/
+
+for (let ctor of ctors) {
+  const rab = CreateResizableArrayBuffer(4 * ctor.BYTES_PER_ELEMENT, 8 * ctor.BYTES_PER_ELEMENT);
+  const fixedLength = new ctor(rab, 0, 4);
+  const fixedLengthWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT, 2);
+  const lengthTracking = new ctor(rab, 0);
+  const lengthTrackingWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT);
+
+  // Write some data into the array.
+  const taWrite = new ctor(rab);
+  for (let i = 0; i < 4; ++i) {
+    WriteToTypedArray(taWrite, i, 2 * i);
+  }
+
+  // Orig. array: [0, 2, 4, 6]
+  //              [0, 2, 4, 6] << fixedLength
+  //                    [4, 6] << fixedLengthWithOffset
+  //              [0, 2, 4, 6, ...] << lengthTracking
+  //                    [4, 6, ...] << lengthTrackingWithOffset
+
+  function ReduceRightCollecting(array) {
+    const reduceRightValues = [];
+    Array.prototype.reduceRight.call(array, (acc, n) => {
+      reduceRightValues.push(n);
+    }, 'initial value');
+    reduceRightValues.reverse();
+    return ToNumbers(reduceRightValues);
+  }
+  assert.compareArray(ReduceRightCollecting(fixedLength), [
+    0,
+    2,
+    4,
+    6
+  ]);
+  assert.compareArray(ReduceRightCollecting(fixedLengthWithOffset), [
+    4,
+    6
+  ]);
+  assert.compareArray(ReduceRightCollecting(lengthTracking), [
+    0,
+    2,
+    4,
+    6
+  ]);
+  assert.compareArray(ReduceRightCollecting(lengthTrackingWithOffset), [
+    4,
+    6
+  ]);
+
+  // Shrink so that fixed length TAs go out of bounds.
+  rab.resize(3 * ctor.BYTES_PER_ELEMENT);
+
+  // Orig. array: [0, 2, 4]
+  //              [0, 2, 4, ...] << lengthTracking
+  //                    [4, ...] << lengthTrackingWithOffset
+
+  assert.compareArray(ReduceRightCollecting(fixedLength), []);
+  assert.compareArray(ReduceRightCollecting(fixedLengthWithOffset), []);
+
+  assert.compareArray(ReduceRightCollecting(lengthTracking), [
+    0,
+    2,
+    4
+  ]);
+  assert.compareArray(ReduceRightCollecting(lengthTrackingWithOffset), [4]);
+
+  // Shrink so that the TAs with offset go out of bounds.
+  rab.resize(1 * ctor.BYTES_PER_ELEMENT);
+  assert.compareArray(ReduceRightCollecting(fixedLength), []);
+  assert.compareArray(ReduceRightCollecting(fixedLengthWithOffset), []);
+
+  assert.compareArray(ReduceRightCollecting(lengthTracking), [0]);
+
+  // Shrink to zero.
+  rab.resize(0);
+  assert.compareArray(ReduceRightCollecting(fixedLength), []);
+  assert.compareArray(ReduceRightCollecting(fixedLengthWithOffset), []);
+  assert.compareArray(ReduceRightCollecting(lengthTrackingWithOffset), []);
+
+  assert.compareArray(ReduceRightCollecting(lengthTracking), []);
+
+  // Grow so that all TAs are back in-bounds.
+  rab.resize(6 * ctor.BYTES_PER_ELEMENT);
+  for (let i = 0; i < 6; ++i) {
+    WriteToTypedArray(taWrite, i, 2 * i);
+  }
+
+  // Orig. array: [0, 2, 4, 6, 8, 10]
+  //              [0, 2, 4, 6] << fixedLength
+  //                    [4, 6] << fixedLengthWithOffset
+  //              [0, 2, 4, 6, 8, 10, ...] << lengthTracking
+  //                    [4, 6, 8, 10, ...] << lengthTrackingWithOffset
+
+  assert.compareArray(ReduceRightCollecting(fixedLength), [
+    0,
+    2,
+    4,
+    6
+  ]);
+  assert.compareArray(ReduceRightCollecting(fixedLengthWithOffset), [
+    4,
+    6
+  ]);
+  assert.compareArray(ReduceRightCollecting(lengthTracking), [
+    0,
+    2,
+    4,
+    6,
+    8,
+    10
+  ]);
+  assert.compareArray(ReduceRightCollecting(lengthTrackingWithOffset), [
+    4,
+    6,
+    8,
+    10
+  ]);
+}

test/built-ins/TypedArray/prototype/reduceRight/resizable-buffer-grow-mid-iteration.js

@@ -0,0 +1,85 @@
+// Copyright 2023 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%typedarray%.prototype.reduceright
+description: >
+  TypedArray.p.reduceRight behaves correctly on TypedArrays backed by resizable
+  buffers that are grown mid-iteration.
+includes: [compareArray.js, resizableArrayBufferUtils.js]
+features: [resizable-arraybuffer]
+---*/
+
+let values;
+let rab;
+let resizeAfter;
+let resizeTo;
+// Collects the view of the resizable array buffer rab into values, with an
+// iteration during which, after resizeAfter steps, rab is resized to length
+// resizeTo. To be called by a method of the view being collected.
+// Note that rab, values, resizeAfter, and resizeTo may need to be reset before
+// calling this.
+function ResizeMidIteration(acc, n) {
+  return CollectValuesAndResize(n, values, rab, resizeAfter, resizeTo);
+}
+
+// Orig. array: [0, 2, 4, 6]
+//              [0, 2, 4, 6] << fixedLength
+//                    [4, 6] << fixedLengthWithOffset
+//              [0, 2, 4, 6, ...] << lengthTracking
+//                    [4, 6, ...] << lengthTrackingWithOffset
+
+// Test for reduceRight.
+
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const fixedLength = new ctor(rab, 0, 4);
+  resizeAfter = 2;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  fixedLength.reduceRight(ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const fixedLengthWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT, 2);
+  resizeAfter = 1;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  fixedLengthWithOffset.reduceRight(ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  resizeAfter = 2;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  lengthTracking.reduceRight(ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const lengthTrackingWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT);
+  resizeAfter = 1;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  lengthTrackingWithOffset.reduceRight(ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}

test/built-ins/TypedArray/prototype/reduceRight/resizable-buffer-shrink-mid-iteration.js

@@ -0,0 +1,101 @@
+// Copyright 2023 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%typedarray%.prototype.reduceright
+description: >
+  TypedArray.p.reduceRight behaves correctly on TypedArrays backed by resizable
+  buffer that is shrunk mid-iteration
+includes: [compareArray.js, resizableArrayBufferUtils.js]
+features: [resizable-arraybuffer]
+---*/
+
+let values;
+let rab;
+let resizeAfter;
+let resizeTo;
+// Collects the view of the resizable array buffer rab into values, with an
+// iteration during which, after resizeAfter steps, rab is resized to length
+// resizeTo. To be called by a method of the view being collected.
+// Note that rab, values, resizeAfter, and resizeTo may need to be reset before
+// calling this.
+function ResizeMidIteration(acc, n) {
+  return CollectValuesAndResize(n, values, rab, resizeAfter, resizeTo);
+}
+
+// Orig. array: [0, 2, 4, 6]
+//              [0, 2, 4, 6] << fixedLength
+//                    [4, 6] << fixedLengthWithOffset
+//              [0, 2, 4, 6, ...] << lengthTracking
+//                    [4, 6, ...] << lengthTrackingWithOffset
+
+// Tests for reduceRight.
+
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const fixedLength = new ctor(rab, 0, 4);
+  resizeAfter = 2;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  fixedLength.reduceRight(ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4,
+    undefined,
+    undefined
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const fixedLengthWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT, 2);
+  resizeAfter = 1;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  fixedLengthWithOffset.reduceRight(ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    undefined
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  resizeAfter = 2;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  // Unaffected by the shrinking, since we've already iterated past the point.
+  lengthTracking.reduceRight(ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  resizeAfter = 1;
+  resizeTo = 2 * ctor.BYTES_PER_ELEMENT;
+  lengthTracking.reduceRight(ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    undefined,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  values = [];
+  rab = CreateRabForTest(ctor);
+  const lengthTrackingWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT);
+  resizeAfter = 1;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  // Unaffected by the shrinking, since we've already iterated past the point.
+  lengthTrackingWithOffset.reduceRight(ResizeMidIteration, 'initial value');
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}

test/built-ins/TypedArray/prototype/reduceRight/resizable-buffer.js

@@ -0,0 +1,146 @@
+// Copyright 2023 the V8 project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-%typedarray%.prototype.reduceright
+description: >
+  TypedArray.p.reduceRight behaves correctly on TypedArrays backed by resizable
+  buffers.
+includes: [compareArray.js, resizableArrayBufferUtils.js]
+features: [resizable-arraybuffer]
+---*/
+
+for (let ctor of ctors) {
+  const rab = CreateResizableArrayBuffer(4 * ctor.BYTES_PER_ELEMENT, 8 * ctor.BYTES_PER_ELEMENT);
+  const fixedLength = new ctor(rab, 0, 4);
+  const fixedLengthWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT, 2);
+  const lengthTracking = new ctor(rab, 0);
+  const lengthTrackingWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT);
+
+  // Write some data into the array.
+  const taWrite = new ctor(rab);
+  for (let i = 0; i < 4; ++i) {
+    WriteToTypedArray(taWrite, i, 2 * i);
+  }
+
+  // Orig. array: [0, 2, 4, 6]
+  //              [0, 2, 4, 6] << fixedLength
+  //                    [4, 6] << fixedLengthWithOffset
+  //              [0, 2, 4, 6, ...] << lengthTracking
+  //                    [4, 6, ...] << lengthTrackingWithOffset
+
+  function ReduceRightCollecting(array) {
+    const reduceRightValues = [];
+    array.reduceRight((acc, n) => {
+      reduceRightValues.push(n);
+    }, 'initial value');
+    reduceRightValues.reverse();
+    return ToNumbers(reduceRightValues);
+  }
+  assert.compareArray(ReduceRightCollecting(fixedLength), [
+    0,
+    2,
+    4,
+    6
+  ]);
+  assert.compareArray(ReduceRightCollecting(fixedLengthWithOffset), [
+    4,
+    6
+  ]);
+  assert.compareArray(ReduceRightCollecting(lengthTracking), [
+    0,
+    2,
+    4,
+    6
+  ]);
+  assert.compareArray(ReduceRightCollecting(lengthTrackingWithOffset), [
+    4,
+    6
+  ]);
+
+  // Shrink so that fixed length TAs go out of bounds.
+  rab.resize(3 * ctor.BYTES_PER_ELEMENT);
+
+  // Orig. array: [0, 2, 4]
+  //              [0, 2, 4, ...] << lengthTracking
+  //                    [4, ...] << lengthTrackingWithOffset
+
+  assert.throws(TypeError, () => {
+    ReduceRightCollecting(fixedLength);
+  });
+  assert.throws(TypeError, () => {
+    ReduceRightCollecting(fixedLengthWithOffset);
+  });
+
+  assert.compareArray(ReduceRightCollecting(lengthTracking), [
+    0,
+    2,
+    4
+  ]);
+  assert.compareArray(ReduceRightCollecting(lengthTrackingWithOffset), [4]);
+
+  // Shrink so that the TAs with offset go out of bounds.
+  rab.resize(1 * ctor.BYTES_PER_ELEMENT);
+  assert.throws(TypeError, () => {
+    ReduceRightCollecting(fixedLength);
+  });
+  assert.throws(TypeError, () => {
+    ReduceRightCollecting(fixedLengthWithOffset);
+  });
+  assert.throws(TypeError, () => {
+    ReduceRightCollecting(lengthTrackingWithOffset);
+  });
+
+  assert.compareArray(ReduceRightCollecting(lengthTracking), [0]);
+
+  // Shrink to zero.
+  rab.resize(0);
+  assert.throws(TypeError, () => {
+    ReduceRightCollecting(fixedLength);
+  });
+  assert.throws(TypeError, () => {
+    ReduceRightCollecting(fixedLengthWithOffset);
+  });
+  assert.throws(TypeError, () => {
+    ReduceRightCollecting(lengthTrackingWithOffset);
+  });
+
+  assert.compareArray(ReduceRightCollecting(lengthTracking), []);
+
+  // Grow so that all TAs are back in-bounds.
+  rab.resize(6 * ctor.BYTES_PER_ELEMENT);
+  for (let i = 0; i < 6; ++i) {
+    WriteToTypedArray(taWrite, i, 2 * i);
+  }
+
+  // Orig. array: [0, 2, 4, 6, 8, 10]
+  //              [0, 2, 4, 6] << fixedLength
+  //                    [4, 6] << fixedLengthWithOffset
+  //              [0, 2, 4, 6, 8, 10, ...] << lengthTracking
+  //                    [4, 6, 8, 10, ...] << lengthTrackingWithOffset
+
+  assert.compareArray(ReduceRightCollecting(fixedLength), [
+    0,
+    2,
+    4,
+    6
+  ]);
+  assert.compareArray(ReduceRightCollecting(fixedLengthWithOffset), [
+    4,
+    6
+  ]);
+  assert.compareArray(ReduceRightCollecting(lengthTracking), [
+    0,
+    2,
+    4,
+    6,
+    8,
+    10
+  ]);
+  assert.compareArray(ReduceRightCollecting(lengthTrackingWithOffset), [
+    4,
+    6,
+    8,
+    10
+  ]);
+}