input: Write a function to return a dictionary with specific keys and values as JSON.
  assert get_data() == {'key1': 'value1', 'key2': 'value2', 'key3': 'value3'}
  assert 'key1' in get_data() and get_data()['key1'] == 'value1'
  assert 'key4' not in get_data()
output: def get_data():
      return {'key1': 'value1', 'key2': 'value2', 'key3': 'value3'}