diff --git a/swh/scanner/tests/flask_api.py b/swh/scanner/tests/flask_api.py
index 5ac7b51..2ab5945 100644
--- a/swh/scanner/tests/flask_api.py
+++ b/swh/scanner/tests/flask_api.py
@@ -1,32 +1,36 @@
 # Copyright (C) 2020  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 from flask import Flask, request
 
 from swh.web.common.exc import LargePayloadExc
 
 from .data import present_swhids
 
 
 def create_app():
     app = Flask(__name__)
 
+    @app.route("/")
+    def index():
+        return "SWH scanner API"
+
     @app.route("/known/", methods=["POST"])
     def known():
         swhids = request.get_json()
 
         if len(swhids) > 900:
             raise LargePayloadExc(
                 "The maximum number of SWHIDs this endpoint can receive is 900"
             )
 
         res = {swhid: {"known": False} for swhid in swhids}
         for swhid in swhids:
             if swhid in present_swhids:
                 res[swhid]["known"] = True
 
         return res
 
     return app
diff --git a/swh/scanner/tests/test_scanner.py b/swh/scanner/tests/test_scanner.py
index 29e1030..c813ea7 100644
--- a/swh/scanner/tests/test_scanner.py
+++ b/swh/scanner/tests/test_scanner.py
@@ -1,117 +1,118 @@
 # Copyright (C) 2020  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
 
 import json
 
+from flask import url_for
 import pytest
 
 from swh.scanner.exceptions import APIError, InvalidDirectoryPath
 from swh.scanner.model import Tree
 from swh.scanner.scanner import extract_regex_objs, get_subpaths, run, swhids_discovery
 
 from .data import correct_api_response, present_swhids, to_exclude_swhid
 
 aio_url = "http://example.org/api/known/"
 
 
 def test_extract_regex_objs(temp_folder):
     root_path = temp_folder["root"]
 
     patterns = (str(temp_folder["subdir"]), "/none")
     sre_patterns = [reg_obj for reg_obj in extract_regex_objs(root_path, patterns)]
     assert len(sre_patterns) == 2
 
     patterns = (*patterns, "/tmp")
     with pytest.raises(InvalidDirectoryPath):
         sre_patterns = [reg_obj for reg_obj in extract_regex_objs(root_path, patterns)]
 
 
 def test_scanner_correct_api_request(mock_aioresponse, event_loop, aiosession):
     mock_aioresponse.post(
         aio_url,
         status=200,
         content_type="application/json",
         body=json.dumps(correct_api_response),
     )
 
     actual_result = event_loop.run_until_complete(
         swhids_discovery([], aiosession, "http://example.org/api/")
     )
 
     assert correct_api_response == actual_result
 
 
 def test_scanner_raise_apierror(mock_aioresponse, event_loop, aiosession):
     mock_aioresponse.post(aio_url, content_type="application/json", status=413)
 
     with pytest.raises(APIError):
         event_loop.run_until_complete(
             swhids_discovery([], aiosession, "http://example.org/api/")
         )
 
 
 def test_scanner_raise_apierror_input_size_limit(event_loop, aiosession, live_server):
 
-    api_url = live_server.url() + "/"
+    api_url = url_for("index", _external=True)
     request = [
         "swh:1:cnt:7c4c57ba9ff496ad179b8f65b1d286edbda34c9a" for i in range(901)
     ]  # /known/ is limited at 900
 
     with pytest.raises(APIError):
         event_loop.run_until_complete(swhids_discovery(request, aiosession, api_url))
 
 
 def test_scanner_get_subpaths(temp_folder):
     root = temp_folder["root"]
 
     actual_result = []
     for subpath, swhid in get_subpaths(root, tuple()):
         # also check if it's a symlink since pytest tmp_dir fixture create
         # also a symlink to each directory inside the tmp_dir path
         if subpath.is_dir() and not subpath.is_symlink():
             actual_result.append((subpath, swhid))
 
     assert len(actual_result) == 2
 
 
 @pytest.mark.options(debug=False)
 def test_app(app):
     assert not app.debug
 
 
 def test_scanner_result(live_server, event_loop, test_sample_folder):
-    api_url = live_server.url() + "/"
+    api_url = url_for("index", _external=True)
     config = {"web-api": {"url": api_url, "auth-token": None}}
 
     source_tree = Tree(test_sample_folder)
     event_loop.run_until_complete(run(config, test_sample_folder, source_tree, set()))
 
     for child_node in source_tree.iterate():
         node_info = list(child_node.attributes.values())[0]
         if node_info["swhid"] in present_swhids:
             assert node_info["known"] is True
         else:
             assert node_info["known"] is False
 
 
 def test_scanner_result_with_exclude_patterns(
     live_server, event_loop, test_sample_folder
 ):
-    api_url = live_server.url() + "/"
+    api_url = url_for("index", _external=True)
     config = {"web-api": {"url": api_url, "auth-token": None}}
 
     patterns = (str(test_sample_folder) + "/toexclude",)
     exclude_pattern = {
         reg_obj for reg_obj in extract_regex_objs(test_sample_folder, patterns)
     }
 
     source_tree = Tree(test_sample_folder)
     event_loop.run_until_complete(
         run(config, test_sample_folder, source_tree, exclude_pattern)
     )
 
     for child_node in source_tree.iterate():
         node_info = list(child_node.attributes.values())[0]
         assert node_info["swhid"] != to_exclude_swhid