modify the code according to the code review comments.
add getLineCount() method for testing
add test for getLineCount()
Bug Fixed: adding an empty task
Pass the test for getCountLine()
Add sort method; update executeComment for handling sort method
add a test for sort(): input: c b a expected: a b c
Add test for sort(): sort Uppercase task
test pass: sort only lowercase and sort only uppercase
Add test case: mix uppercase and lowercase tasks
add test case: empty task list
test cases passed: mix input of uppercase and lowercase; empty task list
add test for searchTask(): empty task list
searchTask: test passed for empty task list
add test for searchTask(): simple finding
Test Fixed for searchTask
searchTask: test passed for simple finding
add test for searchTask(): case-ignoring search
searchTask: test passed for case-ignoring search