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/wrap.js

@@ -0,0 +1,46 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { noop, slice, stubA } from './utils.js';
+import wrap from '../wrap.js';
+
+describe('wrap', function() {
+  it('should create a wrapped function', function() {
+    var p = wrap(lodashStable.escape, function(func, text) {
+      return '<p>' + func(text) + '</p>';
+    });
+
+    assert.strictEqual(p('fred, barney, & pebbles'), '<p>fred, barney, &amp; pebbles</p>');
+  });
+
+  it('should provide correct `wrapper` arguments', function() {
+    var args;
+
+    var wrapped = wrap(noop, function() {
+      args || (args = slice.call(arguments));
+    });
+
+    wrapped(1, 2, 3);
+    assert.deepStrictEqual(args, [noop, 1, 2, 3]);
+  });
+
+  it('should use `_.identity` when `wrapper` is nullish', function() {
+    var values = [, null, undefined],
+        expected = lodashStable.map(values, stubA);
+
+    var actual = lodashStable.map(values, function(value, index) {
+      var wrapped = index ? wrap('a', value) : wrap('a');
+      return wrapped('b', 'c');
+    });
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should use `this` binding of function', function() {
+    var p = wrap(lodashStable.escape, function(func) {
+      return '<p>' + func(this.text) + '</p>';
+    });
+
+    var object = { 'p': p, 'text': 'fred, barney, & pebbles' };
+    assert.strictEqual(object.p(), '<p>fred, barney, &amp; pebbles</p>');
+  });
+});