Coerce findLastIndex and lastIndexOf fromIndex parameter to integer (#4440)

* Enable lastIndexOf, findLast and findLastIndex

* Coerce findLastIndex fromIndex parameter to integer

* Coerce lastIndexOf fromIndex parameter to integer

test/findLastIndex-and-lastIndexOf.test.js

@@ -0,0 +1,72 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { identity, stubZero, falsey } from './utils.js';
+import findLastIndex from '../findLastIndex.js';
+import lastIndexOf from '../lastIndexOf.js';
+
+const methods = {
+  findLastIndex,
+  lastIndexOf
+};
+
+describe('findLastIndex and lastIndexOf', function() {
+  lodashStable.each(['findLastIndex', 'lastIndexOf'], function(methodName) {
+    var array = [1, 2, 3, 1, 2, 3],
+        func = methods[methodName],
+        resolve = methodName == 'findLastIndex' ? lodashStable.curry(lodashStable.eq) : identity;
+
+    it('`_.' + methodName + '` should return the index of the last matched value', function() {
+      assert.strictEqual(func(array, resolve(3)), 5);
+    });
+
+    it('`_.' + methodName + '` should work with a positive `fromIndex`', function() {
+      assert.strictEqual(func(array, resolve(1), 2), 0);
+    });
+
+    it('`_.' + methodName + '` should work with a `fromIndex` >= `length`', function() {
+      var values = [6, 8, Math.pow(2, 32), Infinity],
+          expected = lodashStable.map(values, lodashStable.constant([-1, 3, -1]));
+
+      var actual = lodashStable.map(values, function(fromIndex) {
+        return [
+          func(array, resolve(undefined), fromIndex),
+          func(array, resolve(1), fromIndex),
+          func(array, resolve(''), fromIndex)
+        ];
+      });
+
+      assert.deepStrictEqual(actual, expected);
+    });
+
+    it('`_.' + methodName + '` should work with a negative `fromIndex`', function() {
+      assert.strictEqual(func(array, resolve(2), -3), 1);
+    });
+
+    it('`_.' + methodName + '` should work with a negative `fromIndex` <= `-length`', function() {
+      var values = [-6, -8, -Infinity],
+          expected = lodashStable.map(values, stubZero);
+
+      var actual = lodashStable.map(values, function(fromIndex) {
+        return func(array, resolve(1), fromIndex);
+      });
+
+      assert.deepStrictEqual(actual, expected);
+    });
+
+    it('`_.' + methodName + '` should treat falsey `fromIndex` values correctly', function() {
+      var expected = lodashStable.map(falsey, function(value) {
+        return value === undefined ? 5 : -1;
+      });
+
+      var actual = lodashStable.map(falsey, function(fromIndex) {
+        return func(array, resolve(3), fromIndex);
+      });
+
+      assert.deepStrictEqual(actual, expected);
+    });
+
+    it('`_.' + methodName + '` should coerce `fromIndex` to an integer', function() {
+      assert.strictEqual(func(array, resolve(2), 4.2), 4);
+    });
+  });
+});