add e2e tests for copying files

e2e/copies_files.spec.ts

@@ -0,0 +1,31 @@
+import { test, expect, Page } from '@playwright/test';
+import { host } from './helpers';
+
+test.describe('Basic Functionality', () => {
+  test('should copy files', async ({ page, context }) => {
+    await page.goto(`${host}/n`);
+    await page.waitForSelector('button:has-text("Run Code")');
+
+    // let monaco load
+    await page.waitForTimeout(500);
+
+    await page.click('[data-test-id="input-editor"]');
+    await page.keyboard.type('1 2 3');
+
+    await page.evaluate(
+      `this.monaco.editor.getModels().find(x => x.getLanguageId() === "cpp").setValue(\`code_value\`)`
+    );
+    await page.evaluate(
+      `this.monaco.editor.getModels().find(x => x.getLanguageId() === "plaintext").setValue(\`input_value\`)`
+    );
+
+    // sync with yjs server
+    await page.waitForTimeout(1500);
+
+    await page.goto(page.url() + '/copy');
+    await page.waitForSelector('button:has-text("Run Code")');
+
+    expect(await page.$('text="code_value"')).toBeTruthy();
+    expect(await page.$('text="input_value"')).toBeTruthy();
+  });
+});