diff --git a/weather-app.py b/weather-app.py
new file mode 100644
index 0000000..48c71b5
--- /dev/null
+++ b/weather-app.py
@@ -0,0 +1,310 @@
+import requests
+
+def get_temperature(city_name, api_key):
+    """
+    Fetches the current temperature in Fahrenheit for a given U.S. city
+    using the OpenWeatherMap API.
+
+    Parameters:
+        city_name (str): The name of the U.S. city.
+        api_key (str): Your OpenWeatherMap API key.
+
+    Returns:
+        float: Current temperature in Fahrenheit if successful.
+        None: If an error occurs or the data cannot be retrieved.
+    """
+    if not api_key or not isinstance(api_key, str):
+        print("Error: Invalid or missing API key.")
+        return None
+
+    base_url = "https://api.openweathermap.org/data/2.5/weather"
+    params = {
+        'q': f"{city_name},US",
+        'appid': api_key,
+        'units': 'imperial'
+    }
+
+    try:
+        response = requests.get(base_url, params=params, timeout=10)
+        response.raise_for_status()
+        data = response.json()
+
+        if 'main' in data and 'temp' in data['main']:
+            return data['main']['temp']
+        else:
+            print("Error: Unexpected response structure.")
+            return None
+    except requests.exceptions.HTTPError as http_err:
+        print(f"HTTP error occurred: {http_err}")
+    except requests.exceptions.ConnectionError:
+        print("Error: Network connection error.")
+    except requests.exceptions.Timeout:
+        print("Error: The request timed out.")
+    except requests.exceptions.RequestException as err:
+        print(f"Error: An unexpected error occurred: {err}")
+    except ValueError:
+        print("Error: Failed to parse JSON response.")
+
+    return None
+
+def main():
+    import os
+    api_key = os.getenv('OPENWEATHER_API_KEY')
+    if not api_key:
+        print("Error: Please set the OPENWEATHER_API_KEY environment variable")
+        return
+
+    city = input("Enter a major U.S. city: ").strip()
+    if not city:
+        print("Error: City name cannot be empty")
+        return
+
+    temp = get_temperature(city, api_key)
+    if temp is not None:
+        print(f"The current temperature in {city.title()} is {temp:.1f}°F.")
+    else:
+        print("Sorry, couldn't find weather data for that city.")
+
+if __name__ == "__main__":
+    main()
+
+
+import unittest
+from unittest.mock import patch, Mock, MagicMock
+import requests
+from weather-app import get_temperature, main
+
+
+class TestGetTemperature(unittest.TestCase):
+    """Test cases for the get_temperature function."""
+
+    @patch('weather-app.requests.get')
+    def test_successful_temperature_fetch(self, mock_get):
+        """Test successful temperature retrieval."""
+        # Mock successful API response
+        mock_response = Mock()
+        mock_response.json.return_value = {
+            'main': {'temp': 72.5}
+        }
+        mock_response.raise_for_status = Mock()
+        mock_get.return_value = mock_response
+
+        result = get_temperature("New York", "valid_api_key")
+        
+        self.assertEqual(result, 72.5)
+        mock_get.assert_called_once_with(
+            "https://api.openweathermap.org/data/2.5/weather",
+            params={'q': 'New York,US', 'appid': 'valid_api_key', 'units': 'imperial'},
+            timeout=10
+        )
+
+    @patch('weather-app.requests.get')
+    @patch('builtins.print')
+    def test_invalid_api_key_none(self, mock_print, mock_get):
+        """Test with None API key."""
+        result = get_temperature("Chicago", None)
+        
+        self.assertIsNone(result)
+        mock_print.assert_called_once_with("Error: Invalid or missing API key.")
+        mock_get.assert_not_called()
+
+    @patch('weather-app.requests.get')
+    @patch('builtins.print')
+    def test_invalid_api_key_empty_string(self, mock_print, mock_get):
+        """Test with empty string API key."""
+        result = get_temperature("Chicago", "")
+        
+        self.assertIsNone(result)
+        mock_print.assert_called_once_with("Error: Invalid or missing API key.")
+        mock_get.assert_not_called()
+
+    @patch('weather-app.requests.get')
+    @patch('builtins.print')
+    def test_invalid_api_key_non_string(self, mock_print, mock_get):
+        """Test with non-string API key."""
+        result = get_temperature("Chicago", 12345)
+        
+        self.assertIsNone(result)
+        mock_print.assert_called_once_with("Error: Invalid or missing API key.")
+        mock_get.assert_not_called()
+
+    @patch('weather-app.requests.get')
+    @patch('builtins.print')
+    def test_http_error_401_unauthorized(self, mock_print, mock_get):
+        """Test HTTP 401 Unauthorized error."""
+        mock_response = Mock()
+        mock_response.raise_for_status.side_effect = requests.exceptions.HTTPError("401 Unauthorized")
+        mock_get.return_value = mock_response
+
+        result = get_temperature("Boston", "invalid_key")
+        
+        self.assertIsNone(result)
+        mock_print.assert_called_once()
+        self.assertIn("HTTP error occurred", str(mock_print.call_args))
+
+    @patch('weather-app.requests.get')
+    @patch('builtins.print')
+    def test_http_error_404_not_found(self, mock_print, mock_get):
+        """Test HTTP 404 Not Found error."""
+        mock_response = Mock()
+        mock_response.raise_for_status.side_effect = requests.exceptions.HTTPError("404 Not Found")
+        mock_get.return_value = mock_response
+
+        result = get_temperature("InvalidCity", "valid_key")
+        
+        self.assertIsNone(result)
+        mock_print.assert_called_once()
+        self.assertIn("HTTP error occurred", str(mock_print.call_args))
+
+    @patch('weather-app.requests.get')
+    @patch('builtins.print')
+    def test_connection_error(self, mock_print, mock_get):
+        """Test network connection error."""
+        mock_get.side_effect = requests.exceptions.ConnectionError("Network unreachable")
+
+        result = get_temperature("Seattle", "valid_key")
+        
+        self.assertIsNone(result)
+        mock_print.assert_called_once_with("Error: Network connection error.")
+
+    @patch('weather-app.requests.get')
+    @patch('builtins.print')
+    def test_timeout_error(self, mock_print, mock_get):
+        """Test request timeout."""
+        mock_get.side_effect = requests.exceptions.Timeout("Request timed out")
+
+        result = get_temperature("Miami", "valid_key")
+        
+        self.assertIsNone(result)
+        mock_print.assert_called_once_with("Error: The request timed out.")
+
+    @patch('weather-app.requests.get')
+    @patch('builtins.print')
+    def test_generic_request_exception(self, mock_print, mock_get):
+        """Test generic request exception."""
+        mock_get.side_effect = requests.exceptions.RequestException("Unknown error")
+
+        result = get_temperature("Phoenix", "valid_key")
+        
+        self.assertIsNone(result)
+        mock_print.assert_called_once()
+        self.assertIn("An unexpected error occurred", str(mock_print.call_args))
+
+    @patch('weather-app.requests.get')
+    @patch('builtins.print')
+    def test_json_parsing_error(self, mock_print, mock_get):
+        """Test JSON parsing error."""
+        mock_response = Mock()
+        mock_response.raise_for_status = Mock()
+        mock_response.json.side_effect = ValueError("Invalid JSON")
+        mock_get.return_value = mock_response
+
+        result = get_temperature("Denver", "valid_key")
+        
+        self.assertIsNone(result)
+        mock_print.assert_called_once_with("Error: Failed to parse JSON response.")
+
+    @patch('weather-app.requests.get')
+    @patch('builtins.print')
+    def test_unexpected_response_structure_missing_main(self, mock_print, mock_get):
+        """Test response with missing 'main' key."""
+        mock_response = Mock()
+        mock_response.json.return_value = {'weather': [{'description': 'clear sky'}]}
+        mock_response.raise_for_status = Mock()
+        mock_get.return_value = mock_response
+
+        result = get_temperature("Atlanta", "valid_key")
+        
+        self.assertIsNone(result)
+        mock_print.assert_called_once_with("Error: Unexpected response structure.")
+
+    @patch('weather-app.requests.get')
+    @patch('builtins.print')
+    def test_unexpected_response_structure_missing_temp(self, mock_print, mock_get):
+        """Test response with missing 'temp' key."""
+        mock_response = Mock()
+        mock_response.json.return_value = {'main': {'humidity': 65}}
+        mock_response.raise_for_status = Mock()
+        mock_get.return_value = mock_response
+
+        result = get_temperature("Portland", "valid_key")
+        
+        self.assertIsNone(result)
+        mock_print.assert_called_once_with("Error: Unexpected response structure.")
+
+
+class TestMain(unittest.TestCase):
+    """Test cases for the main function."""
+
+    @patch('weather-app.get_temperature')
+    @patch('builtins.input')
+    @patch('weather-app.os.getenv')
+    @patch('builtins.print')
+    def test_successful_flow(self, mock_print, mock_getenv, mock_input, mock_get_temp):
+        """Test successful execution with valid inputs."""
+        mock_getenv.return_value = "test_api_key"
+        mock_input.return_value = "  San Francisco  "
+        mock_get_temp.return_value = 68.3
+
+        main()
+
+        mock_getenv.assert_called_once_with('OPENWEATHER_API_KEY')
+        mock_input.assert_called_once_with("Enter a major U.S. city: ")
+        mock_get_temp.assert_called_once_with("San Francisco", "test_api_key")
+        mock_print.assert_called_once_with("The current temperature in San Francisco is 68.3°F.")
+
+    @patch('weather-app.os.getenv')
+    @patch('builtins.print')
+    def test_missing_api_key_env_var(self, mock_print, mock_getenv):
+        """Test when OPENWEATHER_API_KEY environment variable is not set."""
+        mock_getenv.return_value = None
+
+        main()
+
+        mock_getenv.assert_called_once_with('OPENWEATHER_API_KEY')
+        mock_print.assert_called_once_with("Error: Please set the OPENWEATHER_API_KEY environment variable")
+
+    @patch('builtins.input')
+    @patch('weather-app.os.getenv')
+    @patch('builtins.print')
+    def test_empty_city_name(self, mock_print, mock_getenv, mock_input):
+        """Test when user enters empty city name."""
+        mock_getenv.return_value = "test_api_key"
+        mock_input.return_value = "   "
+
+        main()
+
+        mock_print.assert_called_once_with("Error: City name cannot be empty")
+
+    @patch('weather-app.get_temperature')
+    @patch('builtins.input')
+    @patch('weather-app.os.getenv')
+    @patch('builtins.print')
+    def test_get_temperature_returns_none(self, mock_print, mock_getenv, mock_input, mock_get_temp):
+        """Test when get_temperature fails and returns None."""
+        mock_getenv.return_value = "test_api_key"
+        mock_input.return_value = "InvalidCity"
+        mock_get_temp.return_value = None
+
+        main()
+
+        mock_get_temp.assert_called_once_with("InvalidCity", "test_api_key")
+        mock_print.assert_called_once_with("Sorry, couldn't find weather data for that city.")
+
+    @patch('weather-app.get_temperature')
+    @patch('builtins.input')
+    @patch('weather-app.os.getenv')
+    @patch('builtins.print')
+    def test_temperature_formatting(self, mock_print, mock_getenv, mock_input, mock_get_temp):
+        """Test temperature output formatting with various values."""
+        mock_getenv.return_value = "test_api_key"
+        mock_input.return_value = "los angeles"
+        mock_get_temp.return_value = 75.678
+
+        main()
+
+        mock_print.assert_called_once_with("The current temperature in Los Angeles is 75.7°F.")
+
+
+if __name__ == '__main__':
+    unittest.main()