Fix ducktape test runner: robust argument handling

- Handle both old and new script versions gracefully
- Default to producer tests when no arguments provided
- Support multiple argument formats:
  * No args: run all producer tests
  * test_type (producer/consumer/producer_sr): run specific test type
  * test_file.py: run specific test file
  * test_method: run specific test method
- Fixes IndexError in Semaphore when script called without arguments
- Backward compatible with existing usage patterns

Author: k-raina

tests/ducktape/run_ducktape_test.py

@@ -56,8 +56,30 @@ def main():
         return 1
 
     # Get test file path (ducktape expects file paths, not module paths)
+    # ROBUST FIX: Handle both old and new script versions
     test_dir = os.path.dirname(os.path.abspath(__file__))
-    test_file = os.path.join(test_dir, "test_producer.py")
+    
+    # Default to producer tests if no arguments provided
+    if len(sys.argv) > 1:
+        # Arguments provided - use the first one as test file or test type
+        arg = sys.argv[1]
+        if arg in ['producer', 'consumer', 'producer_sr']:
+            # New argparse-style argument - map to test file
+            test_files = {
+                'producer': 'test_producer.py',
+                'consumer': 'test_consumer.py', 
+                'producer_sr': 'test_producer_with_schema_registry.py'
+            }
+            test_file = os.path.join(test_dir, test_files[arg])
+        elif arg.endswith('.py'):
+            # Direct test file specified
+            test_file = os.path.join(test_dir, arg)
+        else:
+            # Assume it's a test method name, use default producer file
+            test_file = os.path.join(test_dir, "test_producer.py")
+    else:
+        # No arguments - default to producer tests
+        test_file = os.path.join(test_dir, "test_producer.py")
 
     if not os.path.exists(test_file):
         print(f"ERROR: Test file not found: {test_file}")
@@ -81,13 +103,18 @@ def main():
         test_file
     ]
 
-    # Add specific test if provided as argument
-    if len(sys.argv) > 1:
+    # Add specific test method if provided as second argument
+    if len(sys.argv) > 2:
+        test_method = sys.argv[2]
+        cmd[-1] = f"{test_file}::{test_method}"
+        print(f"Running specific test: {test_method}")
+    elif len(sys.argv) > 1 and not sys.argv[1].endswith('.py') and sys.argv[1] not in ['producer', 'consumer', 'producer_sr']:
+        # First argument is a test method name (old behavior)
         test_method = sys.argv[1]
         cmd[-1] = f"{test_file}::{test_method}"
         print(f"Running specific test: {test_method}")
     else:
-        print("Running all producer tests")
+        print("Running all tests in the file")
 
     print("Command:", " ".join(cmd))
     print()