diff --git a/tests/test_prepare_dashboard_data.py b/tests/test_prepare_dashboard_data.py
new file mode 100644
index 0000000..369a299
--- /dev/null
+++ b/tests/test_prepare_dashboard_data.py
@@ -0,0 +1,47 @@
+import polars as pl
+
+
+def test_returns_dataframe_with_year_filter():
+    from src.utils.data import prepare_dashboard_data
+
+    dff = prepare_dashboard_data(dashboard_year="2025")
+    assert isinstance(dff, pl.DataFrame)
+    assert dff.height == 1
+
+
+def test_year_mismatch_returns_empty():
+    from src.utils.data import prepare_dashboard_data
+
+    dff = prepare_dashboard_data(dashboard_year="2024")
+    assert isinstance(dff, pl.DataFrame)
+    assert dff.height == 0
+
+
+def test_acheteur_id_partial_match():
+    from src.utils.data import prepare_dashboard_data
+
+    dff = prepare_dashboard_data(
+        dashboard_year="2025",
+        dashboard_acheteur_id="12",
+    )
+    assert dff.height == 1
+
+
+def test_departement_in_clause():
+    from src.utils.data import prepare_dashboard_data
+
+    dff = prepare_dashboard_data(
+        dashboard_year="2025",
+        dashboard_acheteur_departement_code=["75", "92"],
+    )
+    assert dff.height == 1
+
+
+def test_montant_min_above_value_excludes_row():
+    from src.utils.data import prepare_dashboard_data
+
+    dff = prepare_dashboard_data(
+        dashboard_year="2025",
+        dashboard_montant_min=1000,
+    )
+    assert dff.height == 0