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/some.js

@@ -0,0 +1,76 @@
+import assert from 'assert';
+import lodashStable from 'lodash';
+import { identity, empties, stubFalse, stubTrue } from './utils.js';
+import some from '../some.js';
+
+describe('some', function() {
+  it('should return `true` if `predicate` returns truthy for any element', function() {
+    assert.strictEqual(some([false, 1, ''], identity), true);
+    assert.strictEqual(some([null, 'a', 0], identity), true);
+  });
+
+  it('should return `false` for empty collections', function() {
+    var expected = lodashStable.map(empties, stubFalse);
+
+    var actual = lodashStable.map(empties, function(value) {
+      try {
+        return some(value, identity);
+      } catch (e) {}
+    });
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should return `true` as soon as `predicate` returns truthy', function() {
+    var count = 0;
+
+    assert.strictEqual(some([null, true, null], function(value) {
+      count++;
+      return value;
+    }), true);
+
+    assert.strictEqual(count, 2);
+  });
+
+  it('should return `false` if `predicate` returns falsey for all elements', function() {
+    assert.strictEqual(some([false, false, false], identity), false);
+    assert.strictEqual(some([null, 0, ''], identity), false);
+  });
+
+  it('should use `_.identity` when `predicate` is nullish', function() {
+    var values = [, null, undefined],
+        expected = lodashStable.map(values, stubFalse);
+
+    var actual = lodashStable.map(values, function(value, index) {
+      var array = [0, 0];
+      return index ? some(array, value) : some(array);
+    });
+
+    assert.deepStrictEqual(actual, expected);
+
+    expected = lodashStable.map(values, stubTrue);
+    actual = lodashStable.map(values, function(value, index) {
+      var array = [0, 1];
+      return index ? some(array, value) : some(array);
+    });
+
+    assert.deepStrictEqual(actual, expected);
+  });
+
+  it('should work with `_.property` shorthands', function() {
+    var objects = [{ 'a': 0, 'b': 0 }, { 'a': 0, 'b': 1 }];
+    assert.strictEqual(some(objects, 'a'), false);
+    assert.strictEqual(some(objects, 'b'), true);
+  });
+
+  it('should work with `_.matches` shorthands', function() {
+    var objects = [{ 'a': 0, 'b': 0 }, { 'a': 1, 'b': 1}];
+    assert.strictEqual(some(objects, { 'a': 0 }), true);
+    assert.strictEqual(some(objects, { 'b': 2 }), false);
+  });
+
+  it('should work as an iteratee for methods like `_.map`', function() {
+    var actual = lodashStable.map([[1]], some);
+    assert.deepStrictEqual(actual, [true]);
+  });
+});