diff --git a/tests/rotomap/test_automark.py b/tests/rotomap/test_automark.py
new file mode 100644
index 00000000..a5c8cb00
--- /dev/null
+++ b/tests/rotomap/test_automark.py
@@ -0,0 +1,32 @@
+"""Test suite for mel.rotomap.relate."""
+
+import mel.rotomap.automark as automark
+
+
+# returns a list of targets with updated radii if there are matching radii sources within error_distance
+def test_targets_with_updated_radii():
+    # Arrange
+    targets = [
+        {"uuid": "1", "x": 0, "y": 0},
+        {"uuid": "2", "x": 1, "y": 1},
+        {"uuid": "3", "x": 2, "y": 2}
+    ]
+    radii_sources = [
+        {"uuid": "4", "radius": 7, "x": 0, "y": 0},
+        {"uuid": "5", "radius": 12, "x": 1, "y": 1},
+        {"uuid": "6", "radius": 18, "x": 2, "y": 2},
+    ]
+    error_distance = 3
+    only_merge = False
+
+    # Act
+    result = automark.merge_in_radiuses(targets, radii_sources, error_distance, only_merge)
+
+    # Assert
+    assert len(result) == 3
+    assert result[0]["uuid"] == "1"
+    assert result[0]["radius"] == 7
+    assert result[1]["uuid"] == "2"
+    assert result[1]["radius"] == 12
+    assert result[2]["uuid"] == "3"
+    assert result[2]["radius"] == 18
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