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/pull-methods.js

@@ -0,0 +1,49 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { _ } from './utils.js';
+
+describe('pull methods', function() {
+  lodashStable.each(['pull', 'pullAll', 'pullAllWith'], function(methodName) {
+    var func = _[methodName],
+        isPull = methodName == 'pull';
+
+    function pull(array, values) {
+      return isPull
+        ? func.apply(undefined, [array].concat(values))
+        : func(array, values);
+    }
+
+    it('`_.' + methodName + '` should modify and return the array', function() {
+      var array = [1, 2, 3],
+          actual = pull(array, [1, 3]);
+
+      assert.strictEqual(actual, array);
+      assert.deepStrictEqual(array, [2]);
+    });
+
+    it('`_.' + methodName + '` should preserve holes in arrays', function() {
+      var array = [1, 2, 3, 4];
+      delete array[1];
+      delete array[3];
+
+      pull(array, [1]);
+      assert.ok(!('0' in array));
+      assert.ok(!('2' in array));
+    });
+
+    it('`_.' + methodName + '` should treat holes as `undefined`', function() {
+      var array = [1, 2, 3];
+      delete array[1];
+
+      pull(array, [undefined]);
+      assert.deepStrictEqual(array, [1, 3]);
+    });
+
+    it('`_.' + methodName + '` should match `NaN`', function() {
+      var array = [1, NaN, 3, NaN];
+
+      pull(array, [NaN]);
+      assert.deepStrictEqual(array, [1, 3]);
+    });
+  });
+});