Add initial test files from lodash v4. (#4172)

* Install test dependencies.

* Add initial test files.

These files were created using a simplistic AST manipulator using `recast` to
preserve formatting. There's bound to be a huge chunk of errors, but this serves
as a good start. QUnit was replaced with Mocha, with ES2015 imports running via
`esm`.

As far as possible, QUnit-specific syntax has been replaced with Mocha's
`describe` and `it`, while the native Node.js `assert` module is used for
assertions. Files in the `test` directory ending in `.test.js` will be treated
as test files.

* Add initial passing files to test run.

test/isTypedArray.js

@@ -0,0 +1,59 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { typedArrays, falsey, stubFalse, args, slice, symbol, realm } from './utils.js';
+import isTypedArray from '../isTypedArray.js';
+
+describe('isTypedArray', function() {
+  it('should return `true` for typed arrays', function() {
+    var expected = lodashStable.map(typedArrays, function(type) {
+      return type in root;
+    });
+
+    var actual = lodashStable.map(typedArrays, function(type) {
+      var Ctor = root[type];
+      return Ctor ? isTypedArray(new Ctor(new ArrayBuffer(8))) : false;
+    });
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should return `false` for non typed arrays', function() {
+    var expected = lodashStable.map(falsey, stubFalse);
+
+    var actual = lodashStable.map(falsey, function(value, index) {
+      return index ? isTypedArray(value) : isTypedArray();
+    });
+
+    assert.deepStrictEqual(actual, expected);
+
+    assert.strictEqual(isTypedArray(args), false);
+    assert.strictEqual(isTypedArray([1, 2, 3]), false);
+    assert.strictEqual(isTypedArray(true), false);
+    assert.strictEqual(isTypedArray(new Date), false);
+    assert.strictEqual(isTypedArray(new Error), false);
+    assert.strictEqual(isTypedArray(_), false);
+    assert.strictEqual(isTypedArray(slice), false);
+    assert.strictEqual(isTypedArray({ 'a': 1 }), false);
+    assert.strictEqual(isTypedArray(1), false);
+    assert.strictEqual(isTypedArray(/x/), false);
+    assert.strictEqual(isTypedArray('a'), false);
+    assert.strictEqual(isTypedArray(symbol), false);
+  });
+
+  it('should work with typed arrays from another realm', function() {
+    if (realm.object) {
+      var props = lodashStable.invokeMap(typedArrays, 'toLowerCase');
+
+      var expected = lodashStable.map(props, function(key) {
+        return realm[key] !== undefined;
+      });
+
+      var actual = lodashStable.map(props, function(key) {
+        var value = realm[key];
+        return value ? isTypedArray(value) : false;
+      });
+
+      assert.deepStrictEqual(actual, expected);
+    }
+  });
+});