diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 8550206..1ed3610 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -9,12 +9,14 @@ build job:
     - apt-get update -qy
     - apt-get install -y python3-dev python3-pip python3.12-venv
     - python3 -V
-    - pip install pdm
-    - pdm install
+    - pip3 install -r requirements.txt
+
     # launch tests
     - export PYTHONPATH=.
     - export FLASK_APP=app
-    - pdm run pytest --cov --cov-report term --cov-report html
+    - pytest tests --cov --cov-report term --cov-report html
+
+
   artifacts:
       paths:
         - src/htmlcov/
diff --git a/src/requirements.txt b/src/requirements.txt
new file mode 100644
index 0000000..8840335
--- /dev/null
+++ b/src/requirements.txt
@@ -0,0 +1,4 @@
+Flask
+flask-wtf
+pytest
+pytest-cov
diff --git a/src/tests/__init__.py b/src/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/src/tests/conftest.py b/src/tests/conftest.py
new file mode 100644
index 0000000..ed58e1a
--- /dev/null
+++ b/src/tests/conftest.py
@@ -0,0 +1,12 @@
+import pytest
+from app import app
+
+# see documentation under https://flask.palletsprojects.com/en/2.0.x/testing/
+
+
+# the client here allow to use the app without running in live server
+# see https://flask.palletsprojects.com/en/2.0.x/testing/#sending-requests-with-the-test-client
+@pytest.fixture
+def client():
+    app.config['TESTING'] = True
+    yield app.test_client()
diff --git a/src/tests/test_api.py b/src/tests/test_api.py
new file mode 100644
index 0000000..e172bc7
--- /dev/null
+++ b/src/tests/test_api.py
@@ -0,0 +1,65 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+
+# Copyright 2023, School of Engineering and Architecture of Fribourg
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from urllib.parse import urlencode
+import json
+
+__author__ = 'Michael Mader'
+__date__ = "2023-03-12"
+__version__ = "0.2"
+__email__ = "michael.maeder@hefr.ch"
+
+
+def call(client, path, params):
+    """calling function that simulates an API webcall of a specific function/route
+    
+    Args:
+        client: this is the client object used by pytest to 'simulate' the API without running the webserver
+        path:   route of the API to use
+        params: GET parameter that are passed to the function
+    
+    Returns:
+        json:   the result of the client call
+    """
+    url = path + '?' + urlencode(params)
+    response = client.get(url)
+    return json.loads(response.data.decode('utf-8'))
+
+# increment test 1
+def test_plus_one1(client):
+    result = call(client, '/inc', {'x': 2})
+    assert result['x'] == 3
+
+# increment test 1
+def test_plus_one2(client):
+    result = call(client, '/inc', {'x': -2})
+    assert result['x'] == -1
+
+# adding test with negative value
+def test_plus_y(client):
+    result = call(client, '/add', {'x': -2, 'y': 7})
+    assert result['result'] == 5
+
+# multiplication test
+def test_multiply(client):
+    result = call(client, '/mul', {'x': -2, 'y': 7})
+    assert result['result'] == -14
+
+# division test
+def test_division(client):
+    result = call(client, '/div', {'x': 35, 'y': 7})
+    assert result['result'] == 5