diff --git a/src/components/source_plate.rs b/src/components/source_plate.rs
index dceba24..fc6bc45 100644
--- a/src/components/source_plate.rs
+++ b/src/components/source_plate.rs
@@ -44,7 +44,7 @@ pub fn SourcePlate(cx: Scope<SourcePlateProps>) -> Element {
 #[inline_props]
 fn SourcePlateCell(cx: Scope<PlateCellProps>, i: u8, j: u8, color: Option<String>) -> Element {
     let selection_state = use_shared_state::<SelectionState>(cx).unwrap();
-    let selected = in_square(
+    let selected = in_rect(
         selection_state.read().m_start,
         selection_state.read().m_end,
         (*i, *j),
@@ -80,7 +80,7 @@ fn SourcePlateCell(cx: Scope<PlateCellProps>, i: u8, j: u8, color: Option<String
     })
 }
 
-fn in_square(corner1: Option<(u8, u8)>, corner2: Option<(u8, u8)>, pt: (u8, u8)) -> bool {
+fn in_rect(corner1: Option<(u8, u8)>, corner2: Option<(u8, u8)>, pt: (u8, u8)) -> bool {
     if let (Some(c1), Some(c2)) = (corner1, corner2) {
         return pt.0 <= u8::max(c1.0, c2.0)
             && pt.0 >= u8::min(c1.0, c2.0)
@@ -117,3 +117,59 @@ fn SourcePlateSelectionController(cx: Scope) -> Element {
         }
     })
 }
+
+#[cfg(test)]
+mod tests {
+    use super::in_rect;
+
+    // in_rect tests
+    #[test]
+    fn test_in_rect1() {
+        // Test in center of rect
+        let c1 = (1,1);
+        let c2 = (10,10);
+        let pt = (5,5);
+        assert!(in_rect(Some(c1), Some(c2), pt));
+        // Order of the corners should not matter:
+        assert!(in_rect(Some(c2), Some(c1), pt));
+    }
+
+    #[test]
+    fn test_in_rect2() {
+        // Test on top/bottom edges of rect
+        let c1 = (1,1);
+        let c2 = (10,10);
+        let pt1 = (1,5);
+        let pt2 = (10,5);
+        assert!(in_rect(Some(c1), Some(c2), pt1));
+        assert!(in_rect(Some(c1), Some(c2), pt2));
+        // Order of the corners should not matter:
+        assert!(in_rect(Some(c2), Some(c1), pt1));
+        assert!(in_rect(Some(c2), Some(c1), pt2));
+    }
+
+    #[test]
+    fn test_in_rect3() {
+        // Test on left/right edges of rect
+        let c1 = (1,1);
+        let c2 = (10,10);
+        let pt1 = (5,1);
+        let pt2 = (5,10);
+        assert!(in_rect(Some(c1), Some(c2), pt1));
+        assert!(in_rect(Some(c1), Some(c2), pt2));
+        // Order of the corners should not matter:
+        assert!(in_rect(Some(c2), Some(c1), pt1));
+        assert!(in_rect(Some(c2), Some(c1), pt2));
+    }
+
+    #[test]
+    fn test_in_rect4() {
+    // Test cases that should fail
+        let c1 = (1,1);
+        let c2 = (10,10);
+        let pt1 = (0,0);
+        let pt2 = (15,15);
+        assert_eq!(false, in_rect(Some(c1), Some(c2), pt1));
+        assert_eq!(false, in_rect(Some(c1), Some(c2), pt2));
+    }
+}