feat: adds variables to store expected and actual department name

Author: AmiyahJo

lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/EmployeeTest.java

@@ -10,10 +10,11 @@ void testGetDepartment() {
         Employee employee = new Employee(12345, "John Doe", "Engineering", 75000);
 
         //Act
-        employee.getDepartment();
+        String actualDepartment = employee.getDepartment();
 
         //Assert
-        assertEquals("Engineering", employee.getDepartment());
+        String expectedDepartment = "Engineering";
+        assertEquals(expectedDepartment, actualDepartment);
     }
 
     @Test