 b/tests/test_download.py
+import os
+import unittest
+from unittest.mock import patch, MagicMock, mock_open, call
+import xml.etree.ElementTree as ET
+from download import download_study_info, get_cancer_trials_list
+class GetCancerTrialsListTestCase(unittest.TestCase):
+    @patch('requests.get')
+    def test_get_cancer_trials_list(self, mock_get):
+        # Mock the response from the requests.get function
+        mock_response = mock_get.return_value
+        mock_response.status_code = 200
+        mock_response.json.return_value = {
+            "FullStudiesResponse": {
+                "FullStudies": [
+                    {
+                        "Study": {
+                            "ProtocolSection": {
+                                "IdentificationModule": {
+                                    "NCTId": "NCT12345678"
+                                }
+                            }
+                        }
+                    },
+                    {
+                        "Study": {
+                            "ProtocolSection": {
+                                "IdentificationModule": {
+                                    "NCTId": "NCT87654321"
+                                }
+                            }
+                        }
+                    }
+                ]
+            }
+        }
+        # Call the function and get the result
+        result = get_cancer_trials_list(max_trials=2)
+        # Assert that the requests.get function was called with the correct URL and parameters
+        mock_get.assert_called_once_with(
+            "https://clinicaltrials.gov/api/query/full_studies",
+            params={
+                "expr": "((cancer) OR (neoplasm)) AND ((interventional) OR (treatment)) AND ((mutation) OR (variant))",
+                "min_rnk": 1,
+                "max_rnk": 100,
+                "fmt": "json",
+                "fields": "NCTId"
+            }
+        )
+        # Assert that the function returns the correct list of NCT IDs
+        self.assertEqual(sorted(result), sorted(["NCT12345678", "NCT87654321"]))
+class DownloadStudyInfoTestCase(unittest.TestCase):
+    @patch('os.path.exists')
+    @patch('requests.get')
+    def test_download_study_info(self, mock_get, mock_exists):
+        # Mock the response from the requests.get function
+        mock_response = mock_get.return_value
+        mock_response.status_code = 200
+        mock_response.text = "<root><eligibility>Age less than 18</eligibility></root>"
+        # Mock the os.path.exists function to return False
+        mock_exists.return_value = False
+        # Create a mock file object that can track what was written to it
+        mock_file = mock_open()
+        with patch('builtins.open', mock_file, create=True):
+            # Call the function and get the result
+            result = download_study_info("NCT000000000")
+        # Assert that the requests.get function was called with the correct URL
+        mock_get.assert_called_once_with("https://clinicaltrials.gov/ct2/show/NCT000000000?displayxml=true")
+        # Assert that the function returns an empty list
+        self.assertEqual(result, [])
+        # Assert that the file was written with the new text
+        mock_file().write.assert_called_once_with("<root><eligibility>Age less than 18</eligibility></root>")
+    @patch('os.path.exists')
+    @patch('requests.get')
+    def test_download_study_info_updates_file(self, mock_get, mock_exists):
+        # Mock the response from the requests.get function
+        mock_response = mock_get.return_value
+        mock_response.status_code = 200
+        mock_response.text = "<root><eligibility>Age more than 18</eligibility></root>"
+        # Mock the os.path.exists function to return True
+        mock_exists.return_value = True
+        # Create a dictionary to store mock file objects for each file path
+        mock_files = {}
+        def side_effect(file_path, mode):
+            # If a mock file object for this file path does not exist, create one
+            if file_path not in mock_files:
+                mock_files[file_path] = mock_open(read_data="<root><eligibility>Age less than 18</eligibility></root>")()
+            return mock_files[file_path]
+        with patch('builtins.open', side_effect=side_effect):
+            # Call the function
+            download_study_info("NCT000000000")
+        # Assert that the file was written with the new text
+        mock_files[f"../data/trials_xmls/NCT000000000.xml"].write.assert_called_once_with("<root><eligibility>Age more than 18</eligibility></root>")
+if __name__ == '__main__':
+    unittest.main()