adb: fix abb test.

Don't hardcode cmd's output.

Bug: http://b/157092201
Test: python3 -m unittest test_device.AbbTest
Change-Id: I7145e8d2a31b1c1b459c1e55af3670b95e653eee
diff --git a/adb/test_device.py b/adb/test_device.py
index f5e4cbb..9f1f403 100755
--- a/adb/test_device.py
+++ b/adb/test_device.py
@@ -82,10 +82,13 @@
 
 class AbbTest(DeviceTest):
     def test_smoke(self):
-        result = subprocess.run(['adb', 'abb'], capture_output=True)
-        self.assertEqual(1, result.returncode)
-        expected_output = b"cmd: No service specified; use -l to list all services\n"
-        self.assertEqual(expected_output, result.stderr)
+        abb = subprocess.run(['adb', 'abb'], capture_output=True)
+        cmd = subprocess.run(['adb', 'shell', 'cmd'], capture_output=True)
+
+        # abb squashes all failures to 1.
+        self.assertEqual(abb.returncode == 0, cmd.returncode == 0)
+        self.assertEqual(abb.stdout, cmd.stdout)
+        self.assertEqual(abb.stderr, cmd.stderr)
 
 class ForwardReverseTest(DeviceTest):
     def _test_no_rebind(self, description, direction_list, direction,