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/memoizeCapped.test.js

@@ -0,0 +1,21 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { identity, MAX_MEMOIZE_SIZE } from './utils.js';
+import _memoizeCapped from '../.internal/memoizeCapped.js';
+
+describe('memoizeCapped', function() {
+  var func = _memoizeCapped;
+
+  it('should enforce a max cache size of `MAX_MEMOIZE_SIZE`', function() {
+    if (func) {
+      var memoized = func(identity),
+          cache = memoized.cache;
+
+      lodashStable.times(MAX_MEMOIZE_SIZE, memoized);
+      assert.strictEqual(cache.size, MAX_MEMOIZE_SIZE);
+
+      memoized(MAX_MEMOIZE_SIZE);
+      assert.strictEqual(cache.size, 1);
+    }
+  });
+});