diff --git a/chimp_chomp/src/postprocessing.rs b/chimp_chomp/src/postprocessing.rs
index 2dec92ea..3e39da06 100644
--- a/chimp_chomp/src/postprocessing.rs
+++ b/chimp_chomp/src/postprocessing.rs
@@ -32,24 +32,26 @@ fn insertion_mask(
     mask
 }
 
-fn optimal_insert_position(insertion_mask: Array2<bool>) -> Result<Point, anyhow::Error> {
-    let mask = Mat::from_exact_iter(
-        insertion_mask
-            .mapv(|pixel| if pixel { std::u8::MAX } else { 0 })
+fn ndarray_mask_into_opencv_mat(mask: Array2<bool>) -> Mat {
+    Mat::from_exact_iter(
+        mask.mapv(|pixel| if pixel { std::u8::MAX } else { 0 })
             .into_iter(),
     )
     .unwrap()
     .reshape_nd(
         1,
-        &insertion_mask
+        &mask
             .shape()
             .iter()
             .map(|&dim| dim as i32)
             .collect::<Vec<_>>(),
     )
-    .unwrap();
+    .unwrap()
+}
+
+fn optimal_insert_position(insertion_mask: Mat) -> Result<Point, anyhow::Error> {
     let mut distances = Mat::default();
-    distance_transform(&mask, &mut distances, DIST_L1, DIST_MASK_3, CV_8U).unwrap();
+    distance_transform(&insertion_mask, &mut distances, DIST_L1, DIST_MASK_3, CV_8U).unwrap();
     let (furthest_point, _) = distances
         .iter::<u8>()
         .unwrap()
@@ -99,7 +101,7 @@ fn postprocess_inference(
     let (crystals, crystal_masks) = find_crystal_instances(&labels, &bboxes, &masks)
         .into_iter()
         .unzip();
-    let insertion_mask = insertion_mask(drop_mask, crystal_masks);
+    let insertion_mask = ndarray_mask_into_opencv_mat(insertion_mask(drop_mask, crystal_masks));
     let insertion_point = optimal_insert_position(insertion_mask)?;
     Ok(Contents {
         drop,
@@ -122,3 +124,43 @@ pub async fn inference_postprocessing(
         Err(err) => error_tx.send((err, job)).unwrap(),
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::optimal_insert_position;
+    use opencv::{
+        core::{Point_, Scalar, CV_8UC1},
+        imgproc::{circle, LINE_8},
+        prelude::Mat,
+    };
+
+    #[test]
+    fn optimal_insert_found() {
+        let mut test_image = Mat::new_nd_with_default(
+            &[1024, 1224],
+            CV_8UC1,
+            Scalar::new(0_f64, 0_f64, 0_f64, std::u8::MAX as f64),
+        )
+        .unwrap();
+        circle(
+            &mut test_image,
+            Point_::new(256, 512),
+            128,
+            Scalar::new(
+                std::u8::MAX as f64,
+                std::u8::MAX as f64,
+                std::u8::MAX as f64,
+                std::u8::MAX as f64,
+            ),
+            -1,
+            LINE_8,
+            0,
+        )
+        .unwrap();
+
+        let position = optimal_insert_position(test_image).unwrap();
+
+        assert_eq!(256, position.x);
+        assert_eq!(512, position.y);
+    }
+}