add: unit tests for get_lake_realtion.py

server/map_handler/get_lake_relation.py

 from server.consts import LAKE_RELATIONS_PATH
 
 
-# Writes contents of a lake json file to the response
 def get_map_data(self, file_name: str, measurement: bool):
+    status_code, map_data = fetch_data(file_name, measurement)
+
+    # Set HTTP headers
+    self.send_response(status_code)
+    self.send_header("Content-type", "application/json")
+    self.end_headers()
+
+    # Write contents of the JSON file to response
+    self.wfile.write(map_data.encode('utf-8'))
+
+
+def fetch_data(file_name: str, measurement: bool) -> (int, str):
     """
-        Reads a map file and writes its contents to the response object.
+        Returns the contents of the requested map file.
 
             Parameters:
-                self (BaseHTTPRequestHandler): A instance of a BaseHTTPRequestHandler
                 file_name (str): The name of the requested file/lake
                 measurement (bool): Whether the file is of type _measurements.json or _div.json
     """
@@ -21,19 +31,10 @@ def get_map_data(self, file_name: str, measurement: bool):
         with open(LAKE_RELATIONS_PATH + file_name + file_type, "r") as file:
             data = file.read()
 
-        # Set HTTP headers
-        self.send_response(200)
-        self.send_header("Content-type", "application/json")
-        self.end_headers()
+        return 200, data
 
-        # Write contents of the JSON file to response
-        self.wfile.write(data.encode('utf-8'))
     except FileNotFoundError:
-        self.send_response(404)
-        self.send_header("Content-type", "application/json")
-        self.end_headers()
+        return 404, []
     except Exception:
-        self.send_response(500)
-        self.send_header("Content-type", "application/json")
-        self.end_headers()
+        return 500, []
 

server/map_handler/unit_tests/test_get_lake_relation.py

+from server.map_handler.get_lake_relation import fetch_data
+
+
+def test_fetch_data_true() -> None:
+    test_lake_name = "Mjøsa"
+
+    status_code, _ = fetch_data(test_lake_name, True)
+
+    assert status_code == 200
+
+
+def test_fetch_data_false() -> None:
+    test_lake_name = "Mjøsa"
+
+    status_code, _ = fetch_data(test_lake_name, False)
+
+    assert status_code == 200
+
+
+def test_fetch_data_no_lake() -> None:
+    test_lake_name = "non-existent-lake"
+
+    status_code, _ = fetch_data(test_lake_name, False)
+
+    assert status_code == 404