diff --git a/packages/apps-engine/tests/server/runtime/deno/bundleLegacyApp.spec.ts b/packages/apps-engine/tests/server/runtime/deno/bundleLegacyApp.spec.ts
new file mode 100644
index 0000000000000..600a6c99f5bd0
--- /dev/null
+++ b/packages/apps-engine/tests/server/runtime/deno/bundleLegacyApp.spec.ts
@@ -0,0 +1,114 @@
+import { AsyncTest, Expect, TestFixture } from 'alsatian';
+
+import type { AppImplements } from '../../../../src/server/compiler/AppImplements';
+import type { IParseAppPackageResult } from '../../../../src/server/compiler/IParseAppPackageResult';
+import { bundleLegacyApp } from '../../../../src/server/runtime/deno/bundler';
+
+function makeAppPackage(classFile: string, files: { [key: string]: string }): IParseAppPackageResult {
+	return {
+		info: {
+			id: 'test-app',
+			name: 'Test App',
+			nameSlug: 'test-app',
+			version: '0.0.1',
+			description: 'Test App',
+			requiredApiVersion: '*',
+			classFile,
+			iconFile: 'icon.png',
+			implements: [],
+			author: { name: 'Test', homepage: 'https://test.com', support: 'https://test.com' },
+		},
+		files,
+		languageContent: {},
+		implemented: {} as AppImplements,
+	};
+}
+
+@TestFixture('bundleLegacyApp')
+export class BundleLegacyAppTestFixture {
+	@AsyncTest('bundles a single-file app into one output file')
+	public async testSingleFileApp() {
+		const appPackage = makeAppPackage('app.js', {
+			'app.js': 'module.exports = { hello: "world" };',
+		});
+
+		await bundleLegacyApp(appPackage);
+
+		// After bundling, files should contain only the single bundled entry
+		Expect(Object.keys(appPackage.files).length).toBe(1);
+		Expect(appPackage.files['app.js']).toBeDefined();
+		Expect(typeof appPackage.files['app.js']).toBe('string');
+		Expect(appPackage.files['app.js'].length).toBeGreaterThan(0);
+	}
+
+	@AsyncTest('includes code from relative imports')
+	public async testRelativeImports() {
+		const appPackage = makeAppPackage('app.js', {
+			'app.js': 'var utils = require("./utils"); module.exports = utils;',
+			'utils.js': 'module.exports = { value: 42 };',
+		});
+
+		await bundleLegacyApp(appPackage);
+
+		Expect(Object.keys(appPackage.files).length).toBe(1);
+		// The bundled output should contain the inlined value from utils.js
+		Expect(appPackage.files['app.js']).toContain('42');
+	}
+
+	@AsyncTest('resolves directory index imports (require("./dir") → dir/index.js)')
+	public async testDirectoryIndexImports() {
+		const appPackage = makeAppPackage('app.js', {
+			'app.js': 'var lib = require("./lib"); module.exports = lib;',
+			'lib/index.js': 'module.exports = { fromIndex: true };',
+		});
+
+		await bundleLegacyApp(appPackage);
+
+		Expect(Object.keys(appPackage.files).length).toBe(1);
+		Expect(appPackage.files['app.js']).toContain('fromIndex');
+	}
+
+	@AsyncTest('marks @rocket.chat/apps-engine/* imports as external')
+	public async testExternalAppsEngineImports() {
+		const appPackage = makeAppPackage('app.js', {
+			'app.js': [
+				'var AppInterface = require("@rocket.chat/apps-engine/definition/AppInterface");',
+				'module.exports = AppInterface;',
+			].join('\n'),
+		});
+
+		await bundleLegacyApp(appPackage);
+
+		Expect(Object.keys(appPackage.files).length).toBe(1);
+		// The apps-engine import should remain as an external require, not be inlined
+		Expect(appPackage.files['app.js']).toContain('@rocket.chat/apps-engine');
+	}
+
+	@AsyncTest('handles deeply nested relative imports')
+	public async testDeeplyNestedImports() {
+		const appPackage = makeAppPackage('app.js', {
+			'app.js': 'var a = require("./commands/run"); module.exports = a;',
+			'commands/run.js': 'var helper = require("../helpers/format"); module.exports = helper;',
+			'helpers/format.js': 'module.exports = { formatted: true };',
+		});
+
+		await bundleLegacyApp(appPackage);
+
+		Expect(Object.keys(appPackage.files).length).toBe(1);
+		Expect(appPackage.files['app.js']).toContain('formatted');
+	}
+
+	@AsyncTest('replaces the files record with only the bundled classFile entry')
+	public async testReplacesFilesRecord() {
+		const appPackage = makeAppPackage('main.js', {
+			'main.js': 'var dep = require("./dep"); module.exports = dep;',
+			'dep.js': 'module.exports = "dep-value";',
+			'unused.js': 'module.exports = "unused";',
+		});
+
+		await bundleLegacyApp(appPackage);
+
+		// Only the classFile key should remain after bundling
+		Expect(Object.keys(appPackage.files)).toEqual(['main.js']);
+	}
+}