test(inject-*): Add and passed inject test.

Author: refirst11

test/inject-client-css.test.ts

@@ -0,0 +1,13 @@
+import { injectClientCSS } from '../src/_internal';
+
+test('injectClientCSS correctly appends style element with expected content', () => {
+  const hash = 'ABC12';
+  const sheet = `.test-class_${hash} { color: red; }`;
+  const context = 'Test Context';
+
+  injectClientCSS(hash, sheet, context);
+
+  const styleElement = document.getElementById(hash);
+  expect(styleElement).not.toBeNull();
+  expect(styleElement?.textContent).toContain(`.test-class_${hash} { color: red; }`);
+});

test/inject-client-global-css.test.ts

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+import { injectClientGlobalCSS } from '../src/_internal';
+
+test('injectClientGlobalCSS correctly appends global style element with expected content', () => {
+  const scoped = 'global-scope';
+  const sheet = '.global-class { color: blue; }';
+
+  injectClientGlobalCSS(sheet, scoped);
+
+  const styleElement = document.querySelector(`[data-scope="${scoped}"]`);
+  expect(styleElement).not.toBeNull();
+  expect(styleElement?.textContent).toContain('.global-class { color: blue; }');
+});

test/inject-server-css.test.ts

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+import { getServerCSS } from '../src/_internal/utils/inject-server-css';
+
+test('returns null when isDevServer is false', () => {
+  // Assuming isDevServer is set to false in this test environment
+  // running the case where isDevServer is true in e2e testing.
+  const injectedCSS = getServerCSS();
+  expect(injectedCSS).toBeNull();
+});