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/defer.test.js

@@ -0,0 +1,40 @@
+import assert from 'assert';
+import { slice } from './utils.js';
+import defer from '../defer.js';
+
+describe('defer', function() {
+  it('should defer `func` execution', function(done) {
+    var pass = false;
+    defer(function() { pass = true; });
+
+    setTimeout(function() {
+      assert.ok(pass);
+      done();
+    }, 32);
+  });
+
+  it('should provide additional arguments to `func`', function(done) {
+    var args;
+
+    defer(function() {
+      args = slice.call(arguments);
+    }, 1, 2);
+
+    setTimeout(function() {
+      assert.deepStrictEqual(args, [1, 2]);
+      done();
+    }, 32);
+  });
+
+  it('should be cancelable', function(done) {
+    var pass = true,
+        timerId = defer(function() { pass = false; });
+
+    clearTimeout(timerId);
+
+    setTimeout(function() {
+      assert.ok(pass);
+      done();
+    }, 32);
+  });
+});