fix: cover join_or_terminate states

* [TEST] Add comprehensive tests for join_or_terminate in ParallelWorkerPool

This commit adds `test_join_or_terminate_mixed_states` and `test_join_or_terminate_empty`
to `tests/test_parallel_processor.py`. These tests verify the emergency shutdown
mechanism in scenarios with multiple processes in different states (hanging, clean exit)
and when the process list is empty.

Co-authored-by: n24q02m <135627235+n24q02m@users.noreply.github.com>

* [TEST] Add comprehensive tests for join_or_terminate in ParallelWorkerPool

This commit adds `test_join_or_terminate_mixed_states` and `test_join_or_terminate_empty`
to `tests/test_parallel_processor.py`. These tests verify the emergency shutdown
mechanism in scenarios with multiple processes in different states (hanging, clean exit)
and when the process list is empty.

Also fixed a formatting issue in `tests/test_parallel_processor.py` flagged by CI.

Co-authored-by: n24q02m <135627235+n24q02m@users.noreply.github.com>

---------

Co-authored-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

Author: n24q02m

tests/test_parallel_processor.py

@@ -560,3 +560,45 @@ def test_process_stream_error_signal():
         list(pool._process_stream([1]))
 
     pool.join_or_terminate.assert_called_once()
+
+
+def test_join_or_terminate_mixed_states():
+    """Test join_or_terminate with multiple processes in different states."""
+    pool = ParallelWorkerPool(worker=SquareWorker, config=PoolConfig(num_workers=3))
+
+    # P1: Finishes immediately
+    p1 = MagicMock()
+    p1.is_alive.return_value = False
+
+    # P2: Hangs and needs termination
+    p2 = MagicMock()
+    p2.is_alive.return_value = True
+
+    # P3: Also hangs
+    p3 = MagicMock()
+    p3.is_alive.return_value = True
+
+    pool.processes = [p1, p2, p3]
+
+    pool.join_or_terminate(timeout=0.1)
+
+    # P1 should have been joined but not terminated
+    p1.join.assert_called_once_with(timeout=0.1)
+    p1.terminate.assert_not_called()
+
+    # P2 and P3 should have been joined AND terminated
+    p2.join.assert_called_once_with(timeout=0.1)
+    p2.terminate.assert_called_once()
+    p3.join.assert_called_once_with(timeout=0.1)
+    p3.terminate.assert_called_once()
+
+    # Processes list should be cleared
+    assert pool.processes == []
+
+
+def test_join_or_terminate_empty():
+    """Test join_or_terminate with no processes."""
+    pool = ParallelWorkerPool(worker=SquareWorker, config=PoolConfig(num_workers=0))
+    pool.processes = []
+    pool.join_or_terminate()
+    assert pool.processes == []