test((*): add union test and fix test name

Author: refirst11

test/create.test.ts

@@ -1,6 +1,6 @@
 import { create } from '../src/core/method/create';
 
-test('Style.create returns an object with string values', () => {
+test('cssx.create returns an object with string values', () => {
   const styleObject = {
     test: {
       color: 'red',

test/style-integration.test.ts test/cssx-integration.test.tstest/style-integration.test.ts renamed to test/cssx-integration.test.ts

@@ -20,3 +20,8 @@ test('cssx.root returns undefined', () => {
   const result = cssx.root({});
   expect(result).toBeUndefined();
 });
+
+test('cssx.union returns a string', () => {
+  const result = cssx.union('test', '', false, undefined);
+  expect(result).toBe('test');
+});

test/global.test.ts

@@ -1,6 +1,6 @@
 import { global } from '../src/core/method/global';
 
-test('Style.global insert style into the head with data-scope="global"', () => {
+test('cssx.global insert style into the head with data-scope="global"', () => {
   global({
     h1: {
       fontSize: 24,

test/root.test.ts

@@ -1,6 +1,6 @@
 import { root } from '../src/core/method/root';
 
-test('Style.root insert style into the head with data-scope="root"', () => {
+test('cssx.root insert style into the head with data-scope="root"', () => {
   root({
     '--color-heading': '#333',
   });

test/set.test.ts

@@ -1,6 +1,6 @@
 import { set } from '../src/core/method/set';
 
-test('Style.set creates a class with correct styles', () => {
+test('cssx.set creates a class with correct styles', () => {
   const styleObject = {
     color: 'blue',
     margin: '10px',