[fuchsia] remove no devices found from ffx parsing (#77651)

dev/devicelab/lib/framework/adb.dart

@@ -395,7 +395,6 @@ class FuchsiaDeviceDiscovery implements DeviceDiscovery {
     final Map<String, HealthCheckResult> results = <String, HealthCheckResult>{};
     for (final String deviceId in await discoverDevices()) {
       try {
-        StringBuffer stderr;
         final int resolveResult = await exec(
           _ffx,
           <String>[
@@ -404,11 +403,9 @@ class FuchsiaDeviceDiscovery implements DeviceDiscovery {
             '--format',
             'a',
             deviceId,
-          ],
-          stderr: stderr
+          ]
         );
-        final String stderrOutput = stderr.toString().trim();
-        if (resolveResult == 0 && ! stderrOutput.contains('No devices found')) {
+        if (resolveResult == 0) {
           results['fuchsia-device-$deviceId'] = HealthCheckResult.success();
         } else {
           results['fuchsia-device-$deviceId'] = HealthCheckResult.failure('Cannot resolve device $deviceId');

dev/devicelab/lib/framework/utils.dart

@@ -322,7 +322,6 @@ Future<int> exec(
   List<String> arguments, {
   Map<String, String> environment,
   bool canFail = false, // as in, whether failures are ok. False means that they are fatal.
-  StringBuffer stderr, // if not null, the stderr will be written here
   String workingDirectory,
 }) async {
   return _execute(
@@ -330,7 +329,6 @@ Future<int> exec(
     arguments,
     environment: environment,
     canFail : canFail,
-    stderr: stderr,
     workingDirectory: workingDirectory,
   );
 }

packages/flutter_tools/lib/src/fuchsia/fuchsia_ffx.dart

@@ -93,9 +93,6 @@ class FuchsiaFfx {
       _logger.printError('ffx failed: ${result.stderr}');
       return null;
     }
-    if (result.stderr.contains('No devices found')) {
-      return null;
-    }
     return result.stdout.trim();
   }
 }

packages/flutter_tools/test/general.shard/fuchsia/fuchsia_ffx_test.dart

@@ -130,6 +130,85 @@ void main() {
           <String>['device1']);
     });
   });
+
+  group('ffx resolve', () {
+    testWithoutContext('ffx not found', () {
+      final FuchsiaFfx fuchsiaFfx = FuchsiaFfx(
+        fuchsiaArtifacts: fakeFuchsiaArtifacts,
+        logger: logger,
+        processManager: FakeProcessManager.any(),
+      );
+
+      expect(() async => fuchsiaFfx.list(),
+          throwsToolExit(message: 'Fuchsia ffx tool not found.'));
+    });
+
+    testWithoutContext('unknown device', () async {
+      ffx.createSync();
+
+      final ProcessManager processManager =
+          FakeProcessManager.list(<FakeCommand>[
+        FakeCommand(
+          command: <String>[ffx.path, 'target', 'list', '--format', 'a', 'unknown-device'],
+          exitCode: 2,
+          stderr: 'No devices found.',
+        ),
+      ]);
+
+      final FuchsiaFfx fuchsiaFfx = FuchsiaFfx(
+        fuchsiaArtifacts: fakeFuchsiaArtifacts,
+        logger: logger,
+        processManager: processManager,
+      );
+
+      expect(await fuchsiaFfx.resolve('unknown-device'), isNull);
+      expect(logger.errorText, 'ffx failed: No devices found.\n');
+    });
+
+    testWithoutContext('error', () async {
+      ffx.createSync();
+
+      final ProcessManager processManager =
+          FakeProcessManager.list(<FakeCommand>[
+        FakeCommand(
+          command: <String>[ffx.path, 'target', 'list', '--format', 'a', 'error-device'],
+          exitCode: 1,
+          stderr: 'unexpected error',
+        ),
+      ]);
+
+      final FuchsiaFfx fuchsiaFfx = FuchsiaFfx(
+        fuchsiaArtifacts: fakeFuchsiaArtifacts,
+        logger: logger,
+        processManager: processManager,
+      );
+
+      expect(await fuchsiaFfx.resolve('error-device'), isNull);
+      expect(logger.errorText, contains('unexpected error'));
+    });
+
+    testWithoutContext('valid device', () async {
+      ffx.createSync();
+
+      final ProcessManager processManager =
+          FakeProcessManager.list(<FakeCommand>[
+        FakeCommand(
+          command: <String>[ffx.path, 'target', 'list', '--format', 'a', 'known-device'],
+          exitCode: 0,
+          stdout: '1234-1234-1234-1234',
+        ),
+      ]);
+
+      final FuchsiaFfx fuchsiaFfx = FuchsiaFfx(
+        fuchsiaArtifacts: fakeFuchsiaArtifacts,
+        logger: logger,
+        processManager: processManager,
+      );
+
+      expect(await fuchsiaFfx.resolve('known-device'), '1234-1234-1234-1234');
+      expect(logger.errorText, isEmpty);
+    });
+  });
 }
 
 class FakeFuchsiaArtifacts extends Fake implements FuchsiaArtifacts {