diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..5f04645
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,25 @@
+name: CI
+on:
+  push:
+    branches: master
+  pull_request:
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    name: Test (Python ${{ matrix.python-version }})
+    strategy:
+      matrix:
+        python-version: ["3.8", "3.9", "3.10", "3.11", "3.12"]
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up Python
+        uses: actions/setup-python@v4
+        with:
+          python-version: "${{ matrix.python-version }}"
+      - name: Install tox
+        run: |
+          python -m pip install --upgrade pip
+          pip install tox tox-gh-actions
+      - name: Run tests
+        run: tox
+
diff --git a/.gitignore b/.gitignore
index 3a78423..d6164aa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,4 @@ __pycache__
 dist
 build
 jellyfin_apiclient_python.egg-info
+.tox
diff --git a/README.md b/README.md
index a48b148..29848a3 100644
--- a/README.md
+++ b/README.md
@@ -60,6 +60,14 @@ client.jellyfin.search_media_items(
 
 For details on what the individual API calls do or how to do a certain task, you will probably find the [Jellyfin MPV Shim](https://github.com/iwalton3/jellyfin-mpv-shim) and [Jellyfin Kodi](https://github.com/jellyfin/jellyfin-kodi) repositories useful.
 
+## Running the tests
+
+The test suite is run via `tox`, and you can install it from PyPi.
+
+ - To run the linter: `tox -elint`
+ - To run the test suite, for Python 3.9: `tox -epy39`
+ - You can run multiple environments, if you wish: `tox -elint,py311`
+
 ## Changes from Jellyfin Kodi
 
  - Removal of `websocket.py` (now a dependency to `websocket_client`).
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_credentials.py b/tests/test_credentials.py
new file mode 100644
index 0000000..af23851
--- /dev/null
+++ b/tests/test_credentials.py
@@ -0,0 +1,84 @@
+import unittest
+
+from jellyfin_apiclient_python.credentials import Credentials
+
+
+class TestCredientials(unittest.TestCase):
+    def setUp(self):
+        self.credentials = Credentials()
+
+    def assertEmptyCredentials(self, credentials):
+        empty_creds = {"Servers": []}
+        self.assertEqual(credentials, empty_creds)
+
+    def test_set_credentials_and_get_credentials(self):
+        credentials = {"Server": "Foo"}
+        self.credentials.set_credentials(credentials)
+        self.assertEqual(self.credentials.get_credentials(), credentials)
+
+    def test_get_credentials(self):
+        empty = self.credentials.get_credentials()
+        self.assertEmptyCredentials(empty)
+
+    def test_set_credentials_evals_to_false(self):
+        self.credentials.set_credentials(False)
+        # get() then swallows the ValueError, and returns empty credentials,
+        # but only if self.credentials evaluates to False
+        self.assertEmptyCredentials(self.credentials.get())
+
+    def test_get(self):
+        empty = self.credentials.get()
+        self.assertEmptyCredentials(empty)
+
+    def test_set(self):
+        data = {"User": "foobar"}
+        self.credentials.set(data)
+        self.assertEqual(self.credentials.get(), data)
+        # Passing anything that evaluates to false will clear it
+        self.credentials.set(False)
+        self.assertEmptyCredentials(self.credentials.get())
+
+    def test_add_update_user(self):
+        server = {}
+        user_data = {"Id": 42}
+        self.credentials.add_update_user(server, user_data)
+        self.assertEqual(server, {"Users": [user_data]})
+        # If we re-add the same user, it is unchanged.
+        self.credentials.add_update_user(server, user_data)
+        self.assertEqual(server, {"Users": [user_data]})
+
+    def test_add_update_server_no_id(self):
+        with self.assertRaises(KeyError):
+            self.credentials.add_update_server({}, {"Foo": "Bar"})
+
+    def test_add_update_server_adds_datelastaccessed(self):
+        servers = []
+        server = {"Id": 42}
+        new_server = self.credentials.add_update_server(servers, server)
+        server["DateLastAccessed"] = "2001-01-01T00:00:00Z"
+        self.assertEqual(new_server, server)
+
+    def test_add_update_server_merges_data(self):
+        # DateLastAccessed must be older for merges to happen
+        servers = [{"Id": 42, "DateLastAccessed": "1999-12-31T23:58:59Z"}]
+        server = {
+            "Id": 42, "AccessToken": "xx", "UserId": 1, "UserLinkType": "Foo",
+            "ExchangeToken": "Bar", "ManualAddress": 2, "LocalAddress": 3,
+            "Name": "Test", "LastConnectionMode": "Unknown",
+            "ConnectServerId": 44
+            }
+        new_server = self.credentials.add_update_server(servers, server)
+        self.assertEqual(new_server, server)
+
+    def test_add_update_server_does_not_merge_if_newer(self):
+        servers = [{"Id": 42, "DateLastAccessed": "2023-10-01T01:02:03Z"}]
+        server = {"Id": 42}
+        new_server = self.credentials.add_update_server(servers, server)
+        self.assertEqual(new_server, servers[0])
+
+    def test_add_update_server_does_not_merge_unknown_fields(self):
+        servers = [{"Id": 42, "DateLastAccessed": "1999-12-31T23:58:59Z"}]
+        server = {"Id": 42, "Foo": "Bar"}
+        new_server = self.credentials.add_update_server(servers, server)
+        merged_server = {"Id": 42, "DateLastAccessed": "2001-01-01T00:00:00Z"}
+        self.assertEqual(new_server, merged_server)
diff --git a/tox.ini b/tox.ini
new file mode 100644
index 0000000..66f9b3a
--- /dev/null
+++ b/tox.ini
@@ -0,0 +1,25 @@
+[tox]
+envlist =
+    lint,
+    py{38,39,310,311,312},
+
+[gh-actions]
+python =
+    3.8: py38
+    3.9: py39
+    3.10: py310, lint
+    3.11: py311
+    3.12: py312
+
+[testenv]
+deps =
+    pytest
+commands = pytest {posargs}
+
+[testenv:lint]
+basepython = python3.10
+skip_install = true
+deps =
+    ruff
+commands =
+    ruff check --exit-non-zero-on-fix jellyfin_apiclient_python tests