remove reuse tags
new unit test case: add tentative task
fix test case: updateTaskWrongType
fix test case confirmTaskNotExist
fix test: updateTaskNotExist
fix test case: confirmTaskNotTentative
fix test case: confirmTaskInvalidDateId
fix test : markTaskNotExist
fix test : deleteNotExistTask
new test case: add conflicting task
new test case: add task deadline has passed
new test case: add wrong task type with multiple deadlines
new test case: help command
new test case: test specific help command
new test case: invalid help command
new test case invalid command
new test case: search keyword does not exist