Please use the following line of code in line 12 of your test class it will result the query results for the for loop in your batch class.

listTask.add(new Task(WhoId=testLead.id,Subject='Call '+i,Type='Unreach Call',Status='Completed'));

The issue is the mismatch of value in type Unreach Call

Please use the following line of code in line 12 of your test class it will result the query results for the for loop in your batch class.

listTask.add(new Task(WhoId=testLead.id,Subject='Call '+i,
                                        Type='Unreach Call',Status='Completed')); 

The issue is the mismatch of value in type Unreach Call