diff --git a/crates/fj-core/src/validate/sketch.rs b/crates/fj-core/src/validate/sketch.rs
index 3d6f6ebf4..f60dc6f49 100644
--- a/crates/fj-core/src/validate/sketch.rs
+++ b/crates/fj-core/src/validate/sketch.rs
@@ -113,84 +113,12 @@ impl SketchValidationError {
 mod tests {
     use crate::{
         assert_contains_err,
-        operations::{
-            build::BuildHalfEdge, build::BuildRegion, insert::Insert,
-        },
+        operations::{build::BuildHalfEdge, insert::Insert},
         topology::{Cycle, HalfEdge, Region, Sketch, Vertex},
         validate::{SketchValidationError, Validate, ValidationError},
         Core,
     };
 
-    #[test]
-    fn should_find_cycle_multiple_references() -> anyhow::Result<()> {
-        let mut core = Core::new();
-
-        let surface = core.layers.topology.surfaces.space_2d();
-
-        let region = <Region as BuildRegion>::circle(
-            [0., 0.],
-            1.,
-            surface.clone(),
-            &mut core,
-        )
-        .insert(&mut core);
-        let valid_sketch = Sketch::new(surface.clone(), vec![region.clone()])
-            .insert(&mut core);
-        valid_sketch.validate_and_return_first_error(&core.layers.geometry)?;
-
-        let shared_cycle = region.exterior();
-        let invalid_sketch = Sketch::new(
-            surface,
-            vec![
-                Region::new(shared_cycle.clone(), vec![]).insert(&mut core),
-                Region::new(shared_cycle.clone(), vec![]).insert(&mut core),
-            ],
-        );
-        assert_contains_err!(
-            core,
-            invalid_sketch,
-            ValidationError::MultipleReferencesToCycle(_)
-        );
-
-        Ok(())
-    }
-
-    #[test]
-    fn should_find_half_edge_multiple_references() -> anyhow::Result<()> {
-        let mut core = Core::new();
-
-        let surface = core.layers.topology.surfaces.space_2d();
-
-        let region = <Region as BuildRegion>::polygon(
-            [[0., 0.], [1., 1.], [0., 1.]],
-            surface.clone(),
-            &mut core,
-        )
-        .insert(&mut core);
-        let valid_sketch = Sketch::new(surface.clone(), vec![region.clone()])
-            .insert(&mut core);
-        valid_sketch.validate_and_return_first_error(&core.layers.geometry)?;
-
-        let exterior = region.exterior();
-        let cloned_edges: Vec<_> =
-            exterior.half_edges().iter().cloned().collect();
-        let interior = Cycle::new(cloned_edges).insert(&mut core);
-
-        let invalid_sketch = Sketch::new(
-            surface,
-            vec![
-                Region::new(exterior.clone(), vec![interior]).insert(&mut core)
-            ],
-        );
-        assert_contains_err!(
-            core,
-            invalid_sketch,
-            ValidationError::MultipleReferencesToHalfEdge(_)
-        );
-
-        Ok(())
-    }
-
     #[test]
     fn should_find_clockwise_exterior_cycle() -> anyhow::Result<()> {
         let mut core = Core::new();
diff --git a/crates/fj-core/src/validation/checks/multiple_references.rs b/crates/fj-core/src/validation/checks/multiple_references.rs
index 24042fa4c..1b73f94bc 100644
--- a/crates/fj-core/src/validation/checks/multiple_references.rs
+++ b/crates/fj-core/src/validation/checks/multiple_references.rs
@@ -104,3 +104,85 @@ impl<T, U> ReferenceCounter<T, U> {
             })
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::{
+        assert_contains_err,
+        operations::{build::BuildRegion, insert::Insert},
+        topology::{Cycle, Region, Sketch},
+        validate::Validate,
+        validation::ValidationError,
+        Core,
+    };
+
+    #[test]
+    fn should_find_cycle_multiple_references() -> anyhow::Result<()> {
+        let mut core = Core::new();
+
+        let surface = core.layers.topology.surfaces.space_2d();
+
+        let region = <Region as BuildRegion>::circle(
+            [0., 0.],
+            1.,
+            surface.clone(),
+            &mut core,
+        )
+        .insert(&mut core);
+        let valid_sketch = Sketch::new(surface.clone(), vec![region.clone()])
+            .insert(&mut core);
+        valid_sketch.validate_and_return_first_error(&core.layers.geometry)?;
+
+        let shared_cycle = region.exterior();
+        let invalid_sketch = Sketch::new(
+            surface,
+            vec![
+                Region::new(shared_cycle.clone(), vec![]).insert(&mut core),
+                Region::new(shared_cycle.clone(), vec![]).insert(&mut core),
+            ],
+        );
+        assert_contains_err!(
+            core,
+            invalid_sketch,
+            ValidationError::MultipleReferencesToCycle(_)
+        );
+
+        Ok(())
+    }
+
+    #[test]
+    fn should_find_half_edge_multiple_references() -> anyhow::Result<()> {
+        let mut core = Core::new();
+
+        let surface = core.layers.topology.surfaces.space_2d();
+
+        let region = <Region as BuildRegion>::polygon(
+            [[0., 0.], [1., 1.], [0., 1.]],
+            surface.clone(),
+            &mut core,
+        )
+        .insert(&mut core);
+        let valid_sketch = Sketch::new(surface.clone(), vec![region.clone()])
+            .insert(&mut core);
+        valid_sketch.validate_and_return_first_error(&core.layers.geometry)?;
+
+        let exterior = region.exterior();
+        let cloned_edges: Vec<_> =
+            exterior.half_edges().iter().cloned().collect();
+        let interior = Cycle::new(cloned_edges).insert(&mut core);
+
+        let invalid_sketch = Sketch::new(
+            surface,
+            vec![
+                Region::new(exterior.clone(), vec![interior]).insert(&mut core)
+            ],
+        );
+        assert_contains_err!(
+            core,
+            invalid_sketch,
+            ValidationError::MultipleReferencesToHalfEdge(_)
+        );
+
+        Ok(())
+    }
+}