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/toArray.test.js

@@ -0,0 +1,48 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { arrayProto, LARGE_ARRAY_SIZE } from './utils.js';
+import toArray from '../toArray.js';
+
+describe('toArray', function() {
+  it('should convert objects to arrays', function() {
+    assert.deepStrictEqual(toArray({ 'a': 1, 'b': 2 }), [1, 2]);
+  });
+
+  it('should convert iterables to arrays', function() {
+    if (Symbol && Symbol.iterator) {
+      var object = { '0': 'a', 'length': 1 };
+      object[Symbol.iterator] = arrayProto[Symbol.iterator];
+
+      assert.deepStrictEqual(toArray(object), ['a']);
+    }
+  });
+
+  it('should convert maps to arrays', function() {
+    if (Map) {
+      var map = new Map;
+      map.set('a', 1);
+      map.set('b', 2);
+      assert.deepStrictEqual(toArray(map), [['a', 1], ['b', 2]]);
+    }
+  });
+
+  it('should convert strings to arrays', function() {
+    assert.deepStrictEqual(toArray(''), []);
+    assert.deepStrictEqual(toArray('ab'), ['a', 'b']);
+    assert.deepStrictEqual(toArray(Object('ab')), ['a', 'b']);
+  });
+
+  it('should work in a lazy sequence', function() {
+    var array = lodashStable.range(LARGE_ARRAY_SIZE + 1);
+
+    var object = lodashStable.zipObject(lodashStable.times(LARGE_ARRAY_SIZE, function(index) {
+      return ['key' + index, index];
+    }));
+
+    var actual = _(array).slice(1).map(String).toArray().value();
+    assert.deepEqual(actual, lodashStable.map(array.slice(1), String));
+
+    actual = _(object).toArray().slice(1).map(String).value();
+    assert.deepEqual(actual, _.map(toArray(object).slice(1), String));
+  });
+});