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/exit-early.js

@@ -0,0 +1,37 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { _ } from './utils.js';
+
+describe('exit early', function() {
+  lodashStable.each(['_baseEach', 'forEach', 'forEachRight', 'forIn', 'forInRight', 'forOwn', 'forOwnRight', 'transform'], function(methodName) {
+    var func = _[methodName];
+
+    it('`_.' + methodName + '` can exit early when iterating arrays', function() {
+      if (func) {
+        var array = [1, 2, 3],
+            values = [];
+
+        func(array, function(value, other) {
+          values.push(lodashStable.isArray(value) ? other : value);
+          return false;
+        });
+
+        assert.deepStrictEqual(values, [lodashStable.endsWith(methodName, 'Right') ? 3 : 1]);
+      }
+    });
+
+    it('`_.' + methodName + '` can exit early when iterating objects', function() {
+      if (func) {
+        var object = { 'a': 1, 'b': 2, 'c': 3 },
+            values = [];
+
+        func(object, function(value, other) {
+          values.push(lodashStable.isArray(value) ? other : value);
+          return false;
+        });
+
+        assert.strictEqual(values.length, 1);
+      }
+    });
+  });
+});