diff --git a/.github/workflows/tests.yaml b/.github/workflows/tests.yaml
index bc3d9a8..874ff08 100644
--- a/.github/workflows/tests.yaml
+++ b/.github/workflows/tests.yaml
@@ -22,10 +22,12 @@ jobs:
         python: ["3.9", "3.10", "3.11", "3.12"]
     steps:
       - uses: actions/checkout@v3
+        with:
+          submodules: true
       - uses: actions/setup-python@v4
         with:
           python-version: ${{ matrix.python }}
       - run: pip install poetry && poetry install
       - run: black --check docs tests decode
-      - run: pytest -v test
+      - run: pytest -v tests
       - run: docs/build
diff --git a/decode/io.py b/decode/io.py
index e69de29..28d7283 100644
--- a/decode/io.py
+++ b/decode/io.py
@@ -0,0 +1,40 @@
+# standard library
+from pathlib import Path
+from typing import Any, Union
+
+
+# dependencies
+import xarray as xr
+
+
+# constants
+NETCDF_SUFFIX = ".nc"
+NETCDF_ENGINE = "scipy"
+ZARR_SUFFIX = ".zarr"
+ZARR_ENGINE = "zarr"
+
+
+# type hints
+PathLike = Union[Path, str]
+
+
+def open_dems(dems: PathLike, **kwargs: Any) -> xr.DataArray:
+    """Open a DEMS file as a DataArray.
+
+    Args:
+        dems: Path of the DEMS file.
+        kwargs: Arguments to be passed to ``xarray.open_dataarray``.
+
+    Return:
+        A DataArray of the opened DEMS file.
+
+    """
+    suffixes = Path(dems).suffixes
+
+    if NETCDF_SUFFIX in suffixes:
+        return xr.open_dataarray(dems, engine=NETCDF_ENGINE, **kwargs)
+
+    if ZARR_SUFFIX in suffixes:
+        return xr.open_dataarray(dems, engine=ZARR_ENGINE, **kwargs)
+
+    raise ValueError(f"Extension of {dems} is not supported.")
diff --git a/tests/test_io.py b/tests/test_io.py
index e69de29..3468e9c 100644
--- a/tests/test_io.py
+++ b/tests/test_io.py
@@ -0,0 +1,18 @@
+# standard library
+from pathlib import Path
+
+
+# dependencies
+from decode import io
+from pytest import mark
+
+
+# constants
+DEMS_DIR = Path(__file__).parents[1] / "data" / "dems"
+DEMS_ALL = map(Path, DEMS_DIR.glob("*.nc.gz"))
+
+
+# test functions
+@mark.parametrize("dems", DEMS_ALL)
+def test_open_dems(dems: Path) -> None:
+    io.open_dems(dems)