Improve Instrumented Python Testing Script

For betting debugging and earlier stop in case of termination, like in
#5754 (comment)

closes #5755

No functional change

tests/testing.py

@@ -150,6 +150,7 @@ def __init__(self):
         self.failed_test_suites = 0
         self.passed_tests = 0
         self.failed_tests = 0
+        self.stop_on_failure = True
 
     def has_failed(self) -> bool:
         return self.failed_test_suites > 0
@@ -167,6 +168,9 @@ def run(self, classes: List[type]) -> bool:
                         self.failed_test_suites += 1
                     else:
                         self.passed_test_suites += 1
+                except Exception as e:
+                    self.failed_test_suites += 1
+                    print(f"\n{RED_COLOR}Error: {e}{RESET_COLOR}")
                 finally:
                     os.chdir(original_cwd)
 
@@ -226,6 +230,10 @@ def __run_test_method(self, test_instance, method: str) -> int:
             if isinstance(e, AssertionError):
                 self.__handle_assertion_error(t0, method)
 
+            if self.stop_on_failure:
+                self.__print_buffer_output(buffer)
+                raise e
+
             fails += 1
         finally:
             self.__print_buffer_output(buffer)
@@ -286,6 +294,11 @@ def __init__(
 
         self.start()
 
+    def _check_process_alive(self):
+        if not self.process or self.process.poll() is not None:
+            print("\n".join(self.output))
+            raise RuntimeError("Stockfish process has terminated")
+
     def start(self):
         if self.cli:
             self.process = subprocess.run(
@@ -314,6 +327,8 @@ def send_command(self, command: str):
         if not self.process:
             raise RuntimeError("Stockfish process is not started")
 
+        self._check_process_alive()
+
         self.process.stdin.write(command + "\n")
         self.process.stdin.flush()
 
@@ -355,6 +370,7 @@ def readline(self):
             raise RuntimeError("Stockfish process is not started")
 
         while True:
+            self._check_process_alive()
             line = self.process.stdout.readline().strip()
             self.output.append(line)