From f070ffc53b00b10a09eed9fd598e4fda0b24a241 Mon Sep 17 00:00:00 2001
From: Matan Lurey <matanlurey@users.noreply.github.com>
Date: Tue, 3 Sep 2024 14:36:24 -0700
Subject: [PATCH] Get reasonable output when a stream test fails. (#154377)
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Debugging https://github.com/flutter/flutter/issues/154268 was hard; when I removed `--disable-dart-dev` I would get the following error from this test:

<img width="627" alt="Screenshot 2024-08-29 at 4 25 43 PM" src="https://github.com/user-attachments/assets/2cc3266e-cc6e-425f-b909-12d7556ff110">

After my change, this is what the error looks like:

<img width="1055" alt="Screenshot 2024-08-29 at 4 26 50 PM" src="https://github.com/user-attachments/assets/8b0ecccc-a7c9-4da7-bf22-15cef24c4cc7">

In general we should embrace more of the test package and matchers when appropriate.
---
 dev/devicelab/test/run_test.dart | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/dev/devicelab/test/run_test.dart b/dev/devicelab/test/run_test.dart
index e06c55f538..a68af4e01a 100644
--- a/dev/devicelab/test/run_test.dart
+++ b/dev/devicelab/test/run_test.dart
@@ -80,9 +80,16 @@ void main() {
         '--no-terminate-stray-dart-processes',
         '-t', 'smoke_test_setup_failure',
       ]);
-      await process.stdout.transform(utf8.decoder).where(
-        (String line) => line.contains('VM service still not ready. It is possible the target has failed')
-      ).first;
+
+      // If this test fails, the reason is usually buried in stderr.
+      final Stream<String> stderr = process.stderr.transform(utf8.decoder);
+      stderr.listen(printOnFailure);
+
+      final Stream<String> stdout = process.stdout.transform(utf8.decoder);
+      await expectLater(
+        stdout,
+        emitsThrough(contains('VM service still not ready. It is possible the target has failed')),
+      );
       expect(process.kill(), isTrue);
     });