Ty work

Created a few test for the ReverseGraph class. Most of the tests I created were just creating a graph with a number of nodes, and then testing that the graph was actually created with that amount of nodes. I tested creating one without any nodes, and also a high number of nodes.
the constructor to complete graph (and i think any graph), throws an argument exception if you pass it a negative number. so right now your test will fail. but this is not a valid test, because throwing an exception in this case is a valid behavior. I have a test already in the complete graph tests to test this, so this test should probably be removed.