wip: code formatting nits continued

test/isUndefined.spec.js

@@ -0,0 +1,41 @@
+import lodashStable from 'lodash';
+import { falsey, args, slice, symbol, realm } from './utils';
+import isUndefined from '../src/isUndefined';
+
+describe('isUndefined', () => {
+    it('should return `true` for `undefined` values', () => {
+        expect(isUndefined()).toBe(true);
+        expect(isUndefined(undefined)).toBe(true);
+    });
+
+    it('should return `false` for non `undefined` values', () => {
+        const expected = lodashStable.map(falsey, (value) => value === undefined);
+
+        const actual = lodashStable.map(falsey, (value, index) =>
+            index ? isUndefined(value) : isUndefined(),
+        );
+
+        expect(actual).toEqual(expected);
+
+        expect(isUndefined(args)).toBe(false);
+        expect(isUndefined([1, 2, 3])).toBe(false);
+        expect(isUndefined(true)).toBe(false);
+        expect(isUndefined(new Date())).toBe(false);
+        expect(isUndefined(new Error())).toBe(false);
+        expect(isUndefined(slice)).toBe(false);
+        expect(isUndefined({ a: 1 })).toBe(false);
+        expect(isUndefined(1)).toBe(false);
+        expect(isUndefined(/x/)).toBe(false);
+        expect(isUndefined('a')).toBe(false);
+
+        if (Symbol) {
+            expect(isUndefined(symbol)).toBe(false);
+        }
+    });
+
+    it('should work with `undefined` from another realm', () => {
+        if (realm.object) {
+            expect(isUndefined(realm.undefined)).toBe(true);
+        }
+    });
+});