Add item tests

[sunga12]

• Added Unit Tests for the Item class based on the requirements

can_be_archived?() in the Item class

• should return true if published_date is older than 10 years
• otherwise, it should return false

move_to_archive() in the Item class

• should change the archived property to true if the result of the can_be_archived?() method is true
• should do nothing if the result of the can_be_archived?() method is false

[batoolfatima2135]

Great job!!