cli: blocking IO for test --help

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

.changeset/smart-elephants-knock.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+The `test` command now ensures that all IO is flushed before exiting when printing `--help`.

packages/cli/src/commands/test.ts

@@ -78,6 +78,10 @@ export default async (_opts: OptionValues, cmd: Command) => {
     process.env.TZ = 'UTC';
   }
 
+  if (args.includes('--help')) {
+    (process.stdout as any)._handle.setBlocking(true);
+  }
+
   // eslint-disable-next-line jest/no-jest-import
   await require('jest').run(args);
 };