Improving diags when Launcher is invisible when the test fails

Test: presubmit
Bug: 187761685
Change-Id: I69a930ef076dbf6cca5af516228ebe689fac91eb
diff --git a/tests/tapl/com/android/launcher3/tapl/LauncherInstrumentation.java b/tests/tapl/com/android/launcher3/tapl/LauncherInstrumentation.java
index c4d46ee..1144dce 100644
--- a/tests/tapl/com/android/launcher3/tapl/LauncherInstrumentation.java
+++ b/tests/tapl/com/android/launcher3/tapl/LauncherInstrumentation.java
@@ -396,12 +396,15 @@
     }
 
     private String getVisiblePackages() {
-        return mDevice.findObjects(getAnyObjectSelector())
+        final String apps = mDevice.findObjects(getAnyObjectSelector())
                 .stream()
                 .map(LauncherInstrumentation::getApplicationPackageSafe)
                 .distinct()
-                .filter(pkg -> pkg != null && !"com.android.systemui".equals(pkg))
+                .filter(pkg -> pkg != null && !SYSTEMUI_PACKAGE.equals(pkg))
                 .collect(Collectors.joining(", "));
+        return !apps.isEmpty()
+                ? "active app: " + apps
+                : "the test doesn't see views from any app, including Launcher";
     }
 
     private static String getApplicationPackageSafe(UiObject2 object) {