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/remove.js

@@ -0,0 +1,80 @@
+import assert from 'assert';
+import { isEven, slice } from './utils.js';
+import remove from '../remove.js';
+
+describe('remove', function() {
+  it('should modify the array and return removed elements', function() {
+    var array = [1, 2, 3, 4],
+        actual = remove(array, isEven);
+
+    assert.deepStrictEqual(array, [1, 3]);
+    assert.deepStrictEqual(actual, [2, 4]);
+  });
+
+  it('should provide correct `predicate` arguments', function() {
+    var argsList = [],
+        array = [1, 2, 3],
+        clone = array.slice();
+
+    remove(array, function(n, index) {
+      var args = slice.call(arguments);
+      args[2] = args[2].slice();
+      argsList.push(args);
+      return isEven(index);
+    });
+
+    assert.deepStrictEqual(argsList, [[1, 0, clone], [2, 1, clone], [3, 2, clone]]);
+  });
+
+  it('should work with `_.matches` shorthands', function() {
+    var objects = [{ 'a': 0, 'b': 1 }, { 'a': 1, 'b': 2 }];
+    remove(objects, { 'a': 1 });
+    assert.deepStrictEqual(objects, [{ 'a': 0, 'b': 1 }]);
+  });
+
+  it('should work with `_.matchesProperty` shorthands', function() {
+    var objects = [{ 'a': 0, 'b': 1 }, { 'a': 1, 'b': 2 }];
+    remove(objects, ['a', 1]);
+    assert.deepStrictEqual(objects, [{ 'a': 0, 'b': 1 }]);
+  });
+
+  it('should work with `_.property` shorthands', function() {
+    var objects = [{ 'a': 0 }, { 'a': 1 }];
+    remove(objects, 'a');
+    assert.deepStrictEqual(objects, [{ 'a': 0 }]);
+  });
+
+  it('should preserve holes in arrays', function() {
+    var array = [1, 2, 3, 4];
+    delete array[1];
+    delete array[3];
+
+    remove(array, function(n) {
+      return n === 1;
+    });
+
+    assert.ok(!('0' in array));
+    assert.ok(!('2' in array));
+  });
+
+  it('should treat holes as `undefined`', function() {
+    var array = [1, 2, 3];
+    delete array[1];
+
+    remove(array, function(n) {
+      return n == null;
+    });
+
+    assert.deepStrictEqual(array, [1, 3]);
+  });
+
+  it('should not mutate the array until all elements to remove are determined', function() {
+    var array = [1, 2, 3];
+
+    remove(array, function(n, index) {
+      return isEven(index);
+    });
+
+    assert.deepStrictEqual(array, [2]);
+  });
+});