We have a cash register. It will use a printer to print purchase records.

We hope that CashRegister.Process() can use Printer.Print() to print Purchase. When the Process(...) method is called, the Print() method should also be called.

However, we don't want to use a real Printer for testing!

At the same time, we'd like to make sure that when Print() is triggered by Process(), the printed content is from the processed Purchase.

If the printer is out of paper, Process() should throw the specified exception.

Use Moq to eliminate all introduced classes just for tests.

• Write the test code for the requirements as stated above ONE BY ONE.
• You can ONLY modify test code, except Question 1.
• Don't use any 3rd-party Mock library until except Question 5.
• Please git commit once after each question is completed (commit message example: test(question1): add test for CashRegister.Process)