dev/bots/test.sh += robustness (#4682)

dev/bots/test.sh

 #!/bin/bash
-set -ex
 
 export PATH="$PWD/bin:$PWD/bin/cache/dart-sdk/bin:$PATH"
 
-die() {
+trap detect_error_on_exit EXIT HUP INT QUIT TERM
+
+detect_error_on_exit() {
+    exit_code=$?
     set +x
-    echo "Error: script exited early due to error"
-    exit 1
+    if [[ $exit_code -ne 0 ]]; then
+        echo "━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━"
+        echo "Error: script exited early due to error ($exit_code)"
+        echo "━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━"
+    fi
 }
 
+set -ex
+
 # analyze all the Dart code in the repo
 flutter analyze --flutter-repo
 
 # verify that the tests actually return failure on failure and success on success
-(cd dev/automated_tests; ! flutter test test_smoke_test/fail_test.dart > /dev/null) || die
-(cd dev/automated_tests; flutter test test_smoke_test/pass_test.dart > /dev/null) || die
+(cd dev/automated_tests; ! flutter test test_smoke_test/fail_test.dart > /dev/null)
+(cd dev/automated_tests; flutter test test_smoke_test/pass_test.dart > /dev/null)
 
 # run tests
 (cd packages/flutter; flutter test)