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/update-methods.js

@@ -0,0 +1,25 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { _ } from './utils.js';
+
+describe('update methods', function() {
+  lodashStable.each(['update', 'updateWith'], function(methodName) {
+    var func = _[methodName],
+        oldValue = 1;
+
+    it('`_.' + methodName + '` should invoke `updater` with the value on `path` of `object`', function() {
+      var object = { 'a': [{ 'b': { 'c': oldValue } }] },
+          expected = oldValue + 1;
+
+      lodashStable.each(['a[0].b.c', ['a', '0', 'b', 'c']], function(path) {
+        func(object, path, function(n) {
+          assert.strictEqual(n, oldValue);
+          return ++n;
+        });
+
+        assert.strictEqual(object.a[0].b.c, expected);
+        object.a[0].b.c = oldValue;
+      });
+    });
+  });
+});