--- a
+++ b/tests/patches/test_visu.py
@@ -0,0 +1,34 @@
+from tests.helpers import FakeSlide
+from pathaia.patches.visu import preview_from_queries
+from pathaia.util.types import Coord
+import numpy as np
+
+
+def test_preview_from_queries():
+    slide = FakeSlide()
+    queries = []
+    min_res = 512
+    cell_size = 20
+    thickness = 2
+    color = (255, 255, 0)
+    size = Coord(256)
+    level = 1
+    size_0 = size * slide.level_downsamples[level]
+    slide_size = Coord(slide.dimensions)
+    thickness = 2 * (thickness // 2) + 1
+    res = slide_size / size_0 * (thickness + cell_size) + thickness
+    thumb_w = max(min_res, res.x)
+    thumb_h = max(min_res, res.y)
+    thumb = np.array(slide.get_thumbnail((thumb_w, thumb_h)).convert("RGB"))
+    assert (
+        preview_from_queries(
+            slide,
+            queries,
+            min_res=min_res,
+            color=color,
+            thickness=thickness,
+            cell_size=cell_size,
+            size_0=size_0,
+        )
+        == thumb
+    ).all()