wip: code formatting nits continued

test/groupBy.spec.js

@@ -0,0 +1,65 @@
+import lodashStable from 'lodash';
+import groupBy from '../src/groupBy';
+
+describe('groupBy', () => {
+    const array = [6.1, 4.2, 6.3];
+
+    it('should transform keys by `iteratee`', () => {
+        const actual = groupBy(array, Math.floor);
+        expect(actual).toEqual({ 4: [4.2], 6: [6.1, 6.3] });
+    });
+
+    it('should use `_.identity` when `iteratee` is nullish', () => {
+        const array = [6, 4, 6];
+        const values = [, null, undefined];
+        const expected = lodashStable.map(values, lodashStable.constant({ 4: [4], 6: [6, 6] }));
+
+        const actual = lodashStable.map(values, (value, index) =>
+            index ? groupBy(array, value) : groupBy(array),
+        );
+
+        expect(actual).toEqual(expected);
+    });
+
+    it('should work with `_.property` shorthands', () => {
+        const actual = groupBy(['one', 'two', 'three'], 'length');
+        expect(actual).toEqual({ 3: ['one', 'two'], 5: ['three'] });
+    });
+
+    it('should only add values to own, not inherited, properties', () => {
+        const actual = groupBy(array, (n) =>
+            Math.floor(n) > 4 ? 'hasOwnProperty' : 'constructor',
+        );
+
+        expect(actual.constructor).toEqual([4.2]);
+        expect(actual.hasOwnProperty).toEqual([6.1, 6.3]);
+    });
+
+    it('should work with a number for `iteratee`', () => {
+        const array = [
+            [1, 'a'],
+            [2, 'a'],
+            [2, 'b'],
+        ];
+
+        assert.deepStrictEqual(groupBy(array, 0), {
+            1: [[1, 'a']],
+            2: [
+                [2, 'a'],
+                [2, 'b'],
+            ],
+        });
+        assert.deepStrictEqual(groupBy(array, 1), {
+            a: [
+                [1, 'a'],
+                [2, 'a'],
+            ],
+            b: [[2, 'b']],
+        });
+    });
+
+    it('should work with an object for `collection`', () => {
+        const actual = groupBy({ a: 6.1, b: 4.2, c: 6.3 }, Math.floor);
+        expect(actual).toEqual({ 4: [4.2], 6: [6.1, 6.3] });
+    });
+});