[ ] Do not copy the classes under test to the test project (if they change in the main project, the copy should also be modified, which is bad practice). Use project references instead (the test project should reference the project containing those classes).
(You can easily add references: Solution Explorer -> right click on the test project -> Add -> Project reference and then select the other project(s).)
(You can easily add references: Solution Explorer -> right click on the test project -> Add -> Project reference and then select the other project(s).)