Resolve "System tests iteration 1"

Closes #62 (closed)

Added test cases for creating and simulating the simple filter used in the first lab for TSTE87. The SFG used in the labs gives output from the SFG as an array, although, our program seems to give these outputs values incrementally. I expect that we will need to change this in the future to be able to plot the output values.

Also refactorized some test cases.

test/test_inputport.py

@@ -45,7 +45,7 @@ def test_connect_then_disconnect(input_port, output_port):
     assert s1.destination is None
 
 def test_connect_used_port_to_new_port(input_port, output_port, output_port2):
-    """Does connecting multiple ports to an inputport throw error?"""
+    """Multiple connections to an input port should throw an error."""
     input_port.connect(output_port)
     with pytest.raises(Exception):
         input_port.connect(output_port2)