Update @BeforeEach and Initialize @AfterEach for every tests

src/main/java/softeng/g4/Main.java

src/test/java/softeng/g4/MainTest.java

src/test/java/softeng/g4/cli/AdminCLITest.java

src/test/java/softeng/g4/cli/ListIOTest.java

src/test/java/softeng/g4/cli/StudentCLITest.java

src/test/java/softeng/g4/cli/TACLITest.java

src/test/java/softeng/g4/user/AdminTest.java

src/test/java/softeng/g4/user/StudentTest.java

src/test/java/softeng/g4/user/TeachingAssistantTest.java