Ports have Ships ;TLDR

As a port operations manager,
So I can best utilise a port,
I want a port to keep track of the ships currently docked.

Challenge

Port now needs to have a ships property. When a Ship docks at a Port, the Port method needs to add that ship to its ships. When a Ship sets sail, the Port method needs to remove that ship from its ships.

To complete this challenge, you will need to:

• Discuss with your classmates how the domain model now looks.
• Create a new test spec for a Port addShip method.
• Write the code that makes this test pass.
• Create a new test spec for a Port removeShip method.
• Write the code that makes this test pass.
• Create a new test Ship > gets added to port on instantiation in the Ship test suite. You'll need to check ship.currentPort.ships to see if it contains your Ship instance.
• Write the code to make this pass. The Ship constructor will need to call the starting port's (this.currentPort) addShip method, passing itself in (remember the current instance is referred to with this).
• Add an extra assertion to the test for Ship > can dock at a different port to test that the Ship's currentPort's ships contains the Ship instance. You'll likely want to assert on ship.currentPort.ships.
• Write the code that makes this test pass.
• Modify the test for Ship > can set sail to test that the Ship's previous currentPort (you can use indexOf on ship.itinerary to find this) no longer contains the Ship instance on its ships property (something like previousPort.ships).
• Write the code that makes this test pass.
• Add, commit with a meaningful message, and push to GitHub.