Add tests

b_asic/GUI/__init__.py

b_asic/GUI/port_button.py

b_asic/GUI/precedence_graph_window.py

b_asic/GUI/properties_window.py

b_asic/GUI/select_sfg_window.py

b_asic/GUI/simulate_sfg_window.py

b_asic/__init__.py

b_asic/codegen/vhdl/entity.py

b_asic/core_operations.py

b_asic/gui_utils/color_button.py

b_asic/save_load_structure.py

b_asic/schedule.py

b_asic/scheduler_gui/__init__.py

b_asic/scheduler_gui/scheduler_event.py

b_asic/scheduler_gui/signal_item.py

b_asic/sfg_generators.py

b_asic/signal.py

b_asic/signal_flow_graph.py

b_asic/special_operations.py

examples/introduction.py