diff --git a/.gitea/workflows/ci.yml b/.gitea/workflows/ci.yml
index 5c69a7f..b5e86e9 100644
--- a/.gitea/workflows/ci.yml
+++ b/.gitea/workflows/ci.yml
@@ -36,6 +36,13 @@ jobs:
               exit(1)
           "
 
+      - name: Run unit tests
+        run: |
+          docker run --rm -v "$PWD":/app -w /app python:3.13-alpine sh -c "
+            pip install --no-cache-dir -r requirements-dev.txt &&
+            pytest -v
+          "
+
       - name: Check deprecation warnings
         run: |
           docker run --rm adguard-cidre:ci python -W error::DeprecationWarning -c "import blocklist_scheduler" 2>&1 | tee deprecation.log || true
diff --git a/.gitignore b/.gitignore
index d0d192d..2ebddc0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,4 @@
 /adguard/*.log
 /tmp/
+__pycache__/
+.pytest_cache/
diff --git a/pytest.ini b/pytest.ini
new file mode 100644
index 0000000..a635c5c
--- /dev/null
+++ b/pytest.ini
@@ -0,0 +1,2 @@
+[pytest]
+pythonpath = .
diff --git a/requirements-dev.txt b/requirements-dev.txt
new file mode 100644
index 0000000..8594477
--- /dev/null
+++ b/requirements-dev.txt
@@ -0,0 +1,4 @@
+requests
+pyyaml
+schedule
+pytest
diff --git a/tests/test_blocklist_scheduler.py b/tests/test_blocklist_scheduler.py
new file mode 100644
index 0000000..3fd64aa
--- /dev/null
+++ b/tests/test_blocklist_scheduler.py
@@ -0,0 +1,41 @@
+import pytest
+
+import blocklist_scheduler as bs
+
+
+def test_backup_first_start_creates_backup_when_missing(tmp_path, monkeypatch):
+    adguard_yaml = tmp_path / "AdGuardHome.yaml"
+    adguard_yaml.write_text("original: config\n")
+    first_backup = tmp_path / "AdGuardHome.yaml.first-start.bak"
+
+    monkeypatch.setattr(bs, "ADGUARD_YAML", adguard_yaml)
+    monkeypatch.setattr(bs, "FIRST_BACKUP", first_backup)
+
+    bs.backup_first_start()
+
+    assert first_backup.read_text() == "original: config\n"
+
+
+def test_backup_first_start_does_not_overwrite_existing_backup(tmp_path, monkeypatch):
+    adguard_yaml = tmp_path / "AdGuardHome.yaml"
+    adguard_yaml.write_text("new: config\n")
+    first_backup = tmp_path / "AdGuardHome.yaml.first-start.bak"
+    first_backup.write_text("pristine: original\n")
+
+    monkeypatch.setattr(bs, "ADGUARD_YAML", adguard_yaml)
+    monkeypatch.setattr(bs, "FIRST_BACKUP", first_backup)
+
+    bs.backup_first_start()
+
+    assert first_backup.read_text() == "pristine: original\n"
+
+
+def test_backup_first_start_raises_if_adguard_yaml_missing(tmp_path, monkeypatch):
+    adguard_yaml = tmp_path / "AdGuardHome.yaml"
+    first_backup = tmp_path / "AdGuardHome.yaml.first-start.bak"
+
+    monkeypatch.setattr(bs, "ADGUARD_YAML", adguard_yaml)
+    monkeypatch.setattr(bs, "FIRST_BACKUP", first_backup)
+
+    with pytest.raises(FileNotFoundError):
+        bs.backup_first_start()