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/property.test.js

@@ -0,0 +1,122 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { noop } from './utils.js';
+import property from '../property.js';
+
+describe('property', function() {
+  it('should create a function that plucks a property value of a given object', function() {
+    var object = { 'a': 1 };
+
+    lodashStable.each(['a', ['a']], function(path) {
+      var prop = property(path);
+      assert.strictEqual(prop.length, 1);
+      assert.strictEqual(prop(object), 1);
+    });
+  });
+
+  it('should pluck deep property values', function() {
+    var object = { 'a': { 'b': 2 } };
+
+    lodashStable.each(['a.b', ['a', 'b']], function(path) {
+      var prop = property(path);
+      assert.strictEqual(prop(object), 2);
+    });
+  });
+
+  it('should pluck inherited property values', function() {
+    function Foo() {}
+    Foo.prototype.a = 1;
+
+    lodashStable.each(['a', ['a']], function(path) {
+      var prop = property(path);
+      assert.strictEqual(prop(new Foo), 1);
+    });
+  });
+
+  it('should work with a non-string `path`', function() {
+    var array = [1, 2, 3];
+
+    lodashStable.each([1, [1]], function(path) {
+      var prop = property(path);
+      assert.strictEqual(prop(array), 2);
+    });
+  });
+
+  it('should preserve the sign of `0`', function() {
+    var object = { '-0': 'a', '0': 'b' },
+        props = [-0, Object(-0), 0, Object(0)];
+
+    var actual = lodashStable.map(props, function(key) {
+      var prop = property(key);
+      return prop(object);
+    });
+
+    assert.deepStrictEqual(actual, ['a', 'a', 'b', 'b']);
+  });
+
+  it('should coerce `path` to a string', function() {
+    function fn() {}
+    fn.toString = lodashStable.constant('fn');
+
+    var expected = [1, 2, 3, 4],
+        object = { 'null': 1, 'undefined': 2, 'fn': 3, '[object Object]': 4 },
+        paths = [null, undefined, fn, {}];
+
+    lodashStable.times(2, function(index) {
+      var actual = lodashStable.map(paths, function(path) {
+        var prop = property(index ? [path] : path);
+        return prop(object);
+      });
+
+      assert.deepStrictEqual(actual, expected);
+    });
+  });
+
+  it('should pluck a key over a path', function() {
+    var object = { 'a.b': 1, 'a': { 'b': 2 } };
+
+    lodashStable.each(['a.b', ['a.b']], function(path) {
+      var prop = property(path);
+      assert.strictEqual(prop(object), 1);
+    });
+  });
+
+  it('should return `undefined` when `object` is nullish', function() {
+    var values = [, null, undefined],
+        expected = lodashStable.map(values, noop);
+
+    lodashStable.each(['constructor', ['constructor']], function(path) {
+      var prop = property(path);
+
+      var actual = lodashStable.map(values, function(value, index) {
+        return index ? prop(value) : prop();
+      });
+
+      assert.deepStrictEqual(actual, expected);
+    });
+  });
+
+  it('should return `undefined` for deep paths when `object` is nullish', function() {
+    var values = [, null, undefined],
+        expected = lodashStable.map(values, noop);
+
+    lodashStable.each(['constructor.prototype.valueOf', ['constructor', 'prototype', 'valueOf']], function(path) {
+      var prop = property(path);
+
+      var actual = lodashStable.map(values, function(value, index) {
+        return index ? prop(value) : prop();
+      });
+
+      assert.deepStrictEqual(actual, expected);
+    });
+  });
+
+  it('should return `undefined` if parts of `path` are missing', function() {
+    var object = {};
+
+    lodashStable.each(['a', 'a[1].b.c', ['a'], ['a', '1', 'b', 'c']], function(path) {
+      var prop = property(path);
+      assert.strictEqual(prop(object), undefined);
+    });
+  });
+});