input: Write a python function to group and merge emails by their subject.
  assert group_and_merge_emails([{'Subject': 'Meeting', 'Body': 'We have a meeting tomorrow.'}, {'Subject': 'Meeting', 'Body': 'Please bring the report.'}]) == [{'Subject': 'Meeting', 'Body': 'We have a meeting tomorrow.\n\nPlease bring the report.'}]
  assert group_and_merge_emails([{'Subject': 'Hello', 'Body': 'Hi there!'}, {'Subject': 'Hello', 'Body': 'How are you?'}]) == [{'Subject': 'Hello', 'Body': 'Hi there!\n\nHow are you?'}]
  assert group_and_merge_emails([{'Subject': 'Update', 'Body': 'The project is on track.'}, {'Subject': 'Update', 'Body': 'Completion is expected next week.'}, {'Subject': 'Reminder', 'Body': 'Submit your timesheets.'}]) == [{'Subject': 'Update', 'Body': 'The project is on track.\n\nCompletion is expected next week.'}, {'Subject': 'Reminder', 'Body': 'Submit your timesheets.'}]
output: def group_and_merge_emails(emails):
      grouped_emails = {}
      for email in emails:
          subject = email['Subject']
          body = email['Body']
          if subject in grouped_emails:
              grouped_emails[subject].append(body)
          else:
              grouped_emails[subject] = [body]
      
      merged_emails = []
      for subject, bodies in grouped_emails.items():
          merged_emails.append({'Subject': subject, 'Body': '\n\n'.join(bodies)})
      
      return merged_emails