✅ success case: fromJson
fromJson failure: CheckedFromJsonException should be thrown.
  ✅ non-exist weather
  ✅ jsonData has wrong key
  ✅ unexpected type of value
  ✅ required property is missing

✅ success case: encode WeatherRequest

✅ success case
failure case
  ✅ invalidParameter error is thrown
  ✅ unknown error is thrown

✅ success case: getWeather()
failure case: getWeather()
  ✅ an unknown error is thrown
  ✅ invalidParameter error is thrown
  ✅ fromJson error case: CheckedFromJsonException should be thrown.
  ✅ received data is not in JSON format

✅ initial screen
after getting the weather
  ✅ when reload button is pressed, cloudy weather and correct temperature should be displayed.
  ✅ when reload button is pressed, sunny weather and correct temperature should be displayed.
  ✅ when reload button is pressed, rainy weather and correct temperature should be displayed.
when an error occurs
  ✅ when fetchWeather() returns failure with invalidParameter error, error dialog and correct message should be visible. Then the dialog is closed by pressing the ok button.
  ✅ when fetchWeather() returns failure with unknown error, error dialog and correct message should be visible.
  ✅ when fetchWeather() returns failure with CheckedFromJsonException or FormatException, 
        error dialog and correct message should be visible.