RAB: Integrate staging tests for the .findLastIndex method (#4129)

* 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.

test/built-ins/Array/prototype/findLastIndex/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.findlastindex
+description: >
+  Array.p.findLastIndex behaves correctly when receiver is backed by resizable
+  buffer that is 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(n) {
+  CollectValuesAndResize(n, values, rab, resizeAfter, resizeTo);
+  return false;
+}
+
+// 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) {
+  rab = CreateRabForTest(ctor);
+  const fixedLength = new ctor(rab, 0, 4);
+  values = [];
+  resizeAfter = 2;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLength, ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const fixedLengthWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT, 2);
+  values = [];
+  resizeAfter = 1;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLengthWithOffset, ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  values = [];
+  resizeAfter = 2;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTracking, ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const lengthTrackingWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT);
+  values = [];
+  resizeAfter = 1;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTrackingWithOffset, ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}

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

@@ -0,0 +1,97 @@
+// 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.findlastindex
+description: >
+  Array.p.findLastIndex behaves correctly when receiver is 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 ResizeBufferMidIteration(n) {
+  CollectValuesAndResize(n, values, rab, resizeAfter, resizeTo);
+  return false;
+}
+
+// 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) {
+  rab = CreateRabForTest(ctor);
+  const fixedLength = new ctor(rab, 0, 4);
+  values = [];
+  resizeAfter = 2;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLength, ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4,
+    undefined,
+    undefined
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const fixedLengthWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT, 2);
+  values = [];
+  resizeAfter = 1;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLengthWithOffset, ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    undefined
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  values = [];
+  resizeAfter = 2;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTracking, ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  values = [];
+  resizeAfter = 1;
+  resizeTo = 2 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTracking, ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    undefined,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const lengthTrackingWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT);
+  values = [];
+  resizeAfter = 1;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTrackingWithOffset, ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}

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

@@ -0,0 +1,88 @@
+// 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.findlastindex
+description: >
+  Array.p.findLastIndex behaves correctly when receiver is backed by resizable
+  buffer
+includes: [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 isTwoOrFour(n) {
+    return n == 2 || n == 4;
+  }
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLength, isTwoOrFour), 2);
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLengthWithOffset, isTwoOrFour), 0);
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTracking, isTwoOrFour), 2);
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTrackingWithOffset, isTwoOrFour), 0);
+
+  // 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.sameValue(Array.prototype.findLastIndex.call(fixedLength, isTwoOrFour), -1);
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLengthWithOffset, isTwoOrFour), -1);
+
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTracking, isTwoOrFour), 2);
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTrackingWithOffset, isTwoOrFour), 0);
+
+  // Shrink so that the TAs with offset go out of bounds.
+  rab.resize(1 * ctor.BYTES_PER_ELEMENT);
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLength, isTwoOrFour), -1);
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLengthWithOffset, isTwoOrFour), -1);
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTrackingWithOffset, isTwoOrFour), -1);
+
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTracking, isTwoOrFour), -1);
+
+  // Shrink to zero.
+  rab.resize(0);
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLength, isTwoOrFour), -1);
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLengthWithOffset, isTwoOrFour), -1);
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTrackingWithOffset, isTwoOrFour), -1);
+
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTracking, isTwoOrFour), -1);
+
+  // Grow so that all TAs are back in-bounds.
+  rab.resize(6 * ctor.BYTES_PER_ELEMENT);
+  for (let i = 0; i < 4; ++i) {
+    WriteToTypedArray(taWrite, i, 0);
+  }
+  WriteToTypedArray(taWrite, 4, 2);
+  WriteToTypedArray(taWrite, 5, 4);
+
+  // Orig. array: [0, 0, 0, 0, 2, 4]
+  //              [0, 0, 0, 0] << fixedLength
+  //                    [0, 0] << fixedLengthWithOffset
+  //              [0, 0, 0, 0, 2, 4, ...] << lengthTracking
+  //                    [0, 0, 2, 4, ...] << lengthTrackingWithOffset
+
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLength, isTwoOrFour), -1);
+  assert.sameValue(Array.prototype.findLastIndex.call(fixedLengthWithOffset, isTwoOrFour), -1);
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTracking, isTwoOrFour), 5);
+  assert.sameValue(Array.prototype.findLastIndex.call(lengthTrackingWithOffset, isTwoOrFour), 3);
+}
+

test/built-ins/TypedArray/prototype/findLastIndex/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-%typedarray%.prototype.findlastindex
+description: >
+  TypedArray.p.findLastIndex behaves correctly when receiver is backed by resizable
+  buffer that is 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(n) {
+  CollectValuesAndResize(n, values, rab, resizeAfter, resizeTo);
+  return false;
+}
+
+// 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) {
+  rab = CreateRabForTest(ctor);
+  const fixedLength = new ctor(rab, 0, 4);
+  values = [];
+  resizeAfter = 2;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(fixedLength.findLastIndex(ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const fixedLengthWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT, 2);
+  values = [];
+  resizeAfter = 1;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(fixedLengthWithOffset.findLastIndex(ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  values = [];
+  resizeAfter = 2;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(lengthTracking.findLastIndex(ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const lengthTrackingWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT);
+  values = [];
+  resizeAfter = 1;
+  resizeTo = 5 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(lengthTrackingWithOffset.findLastIndex(ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}

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

@@ -0,0 +1,97 @@
+// 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.findlastindex
+description: >
+  TypedArray.p.findLastIndex behaves correctly when receiver is 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 ResizeBufferMidIteration(n) {
+  CollectValuesAndResize(n, values, rab, resizeAfter, resizeTo);
+  return false;
+}
+
+// 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) {
+  rab = CreateRabForTest(ctor);
+  const fixedLength = new ctor(rab, 0, 4);
+  values = [];
+  resizeAfter = 2;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(fixedLength.findLastIndex(ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4,
+    undefined,
+    undefined
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const fixedLengthWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT, 2);
+  values = [];
+  resizeAfter = 1;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(fixedLengthWithOffset.findLastIndex(ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    undefined
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  values = [];
+  resizeAfter = 2;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(lengthTracking.findLastIndex(ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const lengthTracking = new ctor(rab, 0);
+  values = [];
+  resizeAfter = 1;
+  resizeTo = 2 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(lengthTracking.findLastIndex(ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    undefined,
+    2,
+    0
+  ]);
+}
+for (let ctor of ctors) {
+  rab = CreateRabForTest(ctor);
+  const lengthTrackingWithOffset = new ctor(rab, 2 * ctor.BYTES_PER_ELEMENT);
+  values = [];
+  resizeAfter = 1;
+  resizeTo = 3 * ctor.BYTES_PER_ELEMENT;
+  assert.sameValue(lengthTrackingWithOffset.findLastIndex(ResizeBufferMidIteration), -1);
+  assert.compareArray(values, [
+    6,
+    4
+  ]);
+}

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

@@ -0,0 +1,102 @@
+// 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.findlastindex
+description: >
+  TypedArray.p.findLastIndex behaves correctly when receiver is backed by resizable
+  buffer
+includes: [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 isTwoOrFour(n) {
+    return n == 2 || n == 4;
+  }
+  assert.sameValue(fixedLength.findLastIndex(isTwoOrFour), 2);
+  assert.sameValue(fixedLengthWithOffset.findLastIndex(isTwoOrFour), 0);
+  assert.sameValue(lengthTracking.findLastIndex(isTwoOrFour), 2);
+  assert.sameValue(lengthTrackingWithOffset.findLastIndex(isTwoOrFour), 0);
+
+  // 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, () => {
+    fixedLength.findLastIndex(isTwoOrFour);
+  });
+  assert.throws(TypeError, () => {
+    fixedLengthWithOffset.findLastIndex(isTwoOrFour);
+  });
+
+  assert.sameValue(lengthTracking.findLastIndex(isTwoOrFour), 2);
+  assert.sameValue(lengthTrackingWithOffset.findLastIndex(isTwoOrFour), 0);
+
+  // Shrink so that the TAs with offset go out of bounds.
+  rab.resize(1 * ctor.BYTES_PER_ELEMENT);
+  assert.throws(TypeError, () => {
+    fixedLength.findLastIndex(isTwoOrFour);
+  });
+  assert.throws(TypeError, () => {
+    fixedLengthWithOffset.findLastIndex(isTwoOrFour);
+  });
+  assert.throws(TypeError, () => {
+    lengthTrackingWithOffset.findLastIndex(isTwoOrFour);
+  });
+
+  assert.sameValue(lengthTracking.findLastIndex(isTwoOrFour), -1);
+
+  // Shrink to zero.
+  rab.resize(0);
+  assert.throws(TypeError, () => {
+    fixedLength.findLastIndex(isTwoOrFour);
+  });
+  assert.throws(TypeError, () => {
+    fixedLengthWithOffset.findLastIndex(isTwoOrFour);
+  });
+  assert.throws(TypeError, () => {
+    lengthTrackingWithOffset.findLastIndex(isTwoOrFour);
+  });
+  assert.sameValue(lengthTracking.findLastIndex(isTwoOrFour), -1);
+
+  // Grow so that all TAs are back in-bounds.
+  rab.resize(6 * ctor.BYTES_PER_ELEMENT);
+  for (let i = 0; i < 4; ++i) {
+    WriteToTypedArray(taWrite, i, 0);
+  }
+  WriteToTypedArray(taWrite, 4, 2);
+  WriteToTypedArray(taWrite, 5, 4);
+
+  // Orig. array: [0, 0, 0, 0, 2, 4]
+  //              [0, 0, 0, 0] << fixedLength
+  //                    [0, 0] << fixedLengthWithOffset
+  //              [0, 0, 0, 0, 2, 4, ...] << lengthTracking
+  //                    [0, 0, 2, 4, ...] << lengthTrackingWithOffset
+
+  assert.sameValue(fixedLength.findLastIndex(isTwoOrFour), -1);
+  assert.sameValue(fixedLengthWithOffset.findLastIndex(isTwoOrFour), -1);
+  assert.sameValue(lengthTracking.findLastIndex(isTwoOrFour), 5);
+  assert.sameValue(lengthTrackingWithOffset.findLastIndex(isTwoOrFour), 3);
+}