add isNegativeZero

test/isNegativeZero.test.js

@@ -0,0 +1,15 @@
+const expect = require('expect');
+const { isNegativeZero } = require('._30s.js');
+
+test('isNegativeZero is a Function', () => {
+  expect(isNegativeZero).toBeInstanceOf(Function);
+});
+test('0 is not a -0', () => {
+  expect(isNegativeZero(0)).toBeFalsy();
+});
+test('-0 is a negative zero', () => {
+  expect(isNegativeZero(-0)).toBeTruthy();
+});
+test('1 is not a negative zero', () => {
+  expect(isNegativeZero(1)).toBeFalsy();
+});