diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 7c4364c..8f05c7c 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -13,10 +13,11 @@ permissions:
 
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ${{ matrix.os }}
     strategy:
       fail-fast: false
       matrix:
+        os: ["ubuntu-latest", "windows-latest"]
         python-version: ["3.11", "3.12", "3.13"]
     steps:
       - uses: actions/checkout@v4
diff --git a/pyproject.toml b/pyproject.toml
index ecba513..a2ac37f 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -64,6 +64,7 @@ select = ["E", "F", "I", "PL", "T20"]
 addopts = ["--verbose"]
 pythonpath = ["src", "tests"]
 testpaths = ["tests"]
+filterwarnings = ["error"]
 
 [tool.uv]
 required-version = "0.7.8"
\ No newline at end of file
diff --git a/src/adrpy/repositories/adr/repository.py b/src/adrpy/repositories/adr/repository.py
index cac98a4..c6dc760 100644
--- a/src/adrpy/repositories/adr/repository.py
+++ b/src/adrpy/repositories/adr/repository.py
@@ -1,4 +1,3 @@
-import re
 from typing import Final
 
 from adrpy.injection import lidi
@@ -26,12 +25,13 @@ def create(self, adr_name: str, template: RenderedTemplate) -> None:
     def get_next_ordinal_number(self) -> int:
         ordinal_number = 0
         for path in self.SETTINGS.adr_dir.glob("*.md"):
+            # TODO: Use front matter (metadata) to store ordinal number
             filename = path.stem
-            maybe_number_prefix = re.findall(r"\d+", filename)
-            if not maybe_number_prefix:
+            parts = filename.split("-", 1)
+            if not parts or not parts[0].isdigit():
                 continue
-            if (prefix_as_int := int(maybe_number_prefix[0])) > ordinal_number:
-                ordinal_number = prefix_as_int
+            prefix_as_int = int(parts[0])
+            ordinal_number = max(ordinal_number, prefix_as_int)
         return ordinal_number + 1
 
     @staticmethod
diff --git a/tests/fixtures/repository.py b/tests/fixtures/repository.py
index 4362d38..8378a1a 100644
--- a/tests/fixtures/repository.py
+++ b/tests/fixtures/repository.py
@@ -10,8 +10,8 @@
 from adrpy.shared_kernel.settings import Settings
 
 TEST_DIRECTORY = Path(__file__).parent / "testdir"
-TEST_FILENAME = "testfile"
-TEST_FILENAME_WITH_EXTENSION = "testfile.md"
+TEST_FILENAME = "0001-testfile"
+TEST_FILENAME_WITH_EXTENSION = "0001-testfile.md"
 
 
 @pytest.fixture()
diff --git a/tests/integration/repositories/implementation/test_adr_file_repository.py b/tests/integration/repositories/implementation/test_adr_file_repository.py
deleted file mode 100644
index e69de29..0000000
diff --git a/tests/integration/repository/implementation/test_adr_file_repository.py b/tests/integration/repository/implementation/test_adr_file_repository.py
index d18233e..40886d5 100644
--- a/tests/integration/repository/implementation/test_adr_file_repository.py
+++ b/tests/integration/repository/implementation/test_adr_file_repository.py
@@ -32,7 +32,9 @@ def test_should_get_template_file(adr_repository: IADRRepository) -> None:
     assert template.content
 
 
-def test_should_create_file_in_nested_directories(lidi: Lidi) -> None:
+def test_should_create_file_in_nested_directories(
+    lidi: Lidi, adr_repository: IADRRepository
+) -> None:
     # Given
     nested_dir = TEST_DIRECTORY / "nested1" / "nested2"
     new_settings = dataclasses.replace(lidi.resolve(Settings), initial_adr_dir=nested_dir)
@@ -40,10 +42,23 @@ def test_should_create_file_in_nested_directories(lidi: Lidi) -> None:
     rendered_template = RenderedTemplate(name=TEST_FILENAME, content="TEST_CONTENT")
 
     # When
-    lidi.resolve(IADRRepository).create(adr_name=rendered_template.name, template=rendered_template)
+    adr_repository.create(adr_name=rendered_template.name, template=rendered_template)
 
     # Then
     with open(nested_dir / TEST_FILENAME_WITH_EXTENSION, "r") as created_file:
         content = created_file.read()
 
     assert content == rendered_template.content
+
+
+def test_should_get_next_ordinal_number(adr_repository: IADRRepository) -> None:
+    # Given
+    rendered_template = RenderedTemplate(name=TEST_FILENAME, content="TEST_CONTENT")
+    adr_repository.create(adr_name=TEST_FILENAME, template=rendered_template)
+    expected_next_ordinal_number = 2
+
+    # When
+    ordinal_number = adr_repository.get_next_ordinal_number()
+
+    # Then
+    assert ordinal_number == expected_next_ordinal_number