fix(tests): Add test case for getFileListHeaders reactivity

Signed-off-by: Ferdinand Thiessen <opensource@fthiessen.de>

__tests__/fileListHeaders.spec.ts

@@ -32,6 +32,7 @@ describe('FileListHeader init', () => {
 
 		expect(header.id).toBe('test')
 		expect(header.order).toBe(1)
+		// eslint-disable-next-line @typescript-eslint/no-non-null-assertion
 		expect(header.enabled!({} as Folder, {})).toBe(true)
 
 		registerFileListHeaders(header)
@@ -42,6 +43,28 @@ describe('FileListHeader init', () => {
 		expect(logger.debug).toHaveBeenCalled()
 	})
 
+	test('getFileListHeaders() returned array is reactive', () => {
+		logger.debug = vi.fn()
+
+		const headers = getFileListHeaders()
+		// is empty for now
+		expect(headers).toHaveLength(0)
+
+		const header = new Header({
+			id: 'test',
+			order: 1,
+			enabled: () => true,
+			render: () => {},
+			updated: () => {},
+		})
+
+		registerFileListHeaders(header)
+
+		// Now the array changed as it should be reactive
+		expect(headers).toHaveLength(1)
+		expect(headers[0]).toStrictEqual(header)
+	})
+
 	test('Duplicate Header gets rejected', () => {
 		logger.error = vi.fn()
 		const header = new Header({