Changed test layout and refactorized some tests for OutputPort

test/conftest.py

test/fixtures/operation_tree.py

test/fixtures/port.py

test/graph_id/test_graph_id_generator.py

test/port/test_outputport.py

test/signal_flow_graph/test_signal_flow_graph.py

test/test_core_operations.py

test/test_graph_id_generator.py

test/test_inputport.py

test/test_operation.py

test/test_outputport.py

test/test_signal.py

test/traverse/test_traverse_tree.py