diff --git a/.circleci/config.yml b/.circleci/config.yml
index 1a4824038..52b94a5af 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -44,7 +44,6 @@ jobs:
             - ~/.m2
           key: v1-dependencies-{{ checksum "common/deps.edn"}}
 
-
   test-frontend:
     docker:
       - image: penpotapp/devenv:latest
@@ -93,7 +92,6 @@ jobs:
             - ~/.m2
           key: v1-dependencies-{{ checksum "frontend/deps.edn"}}
 
-
   test-integration:
     docker:
       - image: penpotapp/devenv:latest
@@ -180,7 +178,6 @@ jobs:
             - ~/.m2
           key: v1-dependencies-{{ checksum "backend/deps.edn" }}
 
-
   test-exporter:
     docker:
       - image: penpotapp/devenv:latest
@@ -210,6 +207,29 @@ jobs:
             yarn run fmt:clj:check
             yarn run lint:clj
 
+  test-render-wasm:
+    docker:
+      - image: penpotapp/devenv:latest
+
+    working_directory: ~/repo
+    resource_class: medium+
+    environment:
+
+    steps:
+      - checkout
+
+      - run:
+          name: "fmt check"
+          working_directory: "./render-wasm"
+          command: |
+            cargo fmt --check
+
+      - run:
+          name: "cargo tests"
+          working_directory: "./render-wasm"
+          command: |
+            cargo test
+
 workflows:
   penpot:
     jobs:
@@ -218,3 +238,4 @@ workflows:
       - test-backend
       - test-common
       - test-exporter
+      - test-render-wasm
diff --git a/render-wasm/src/shapes.rs b/render-wasm/src/shapes.rs
index 84db1bcda..b095c2fa6 100644
--- a/render-wasm/src/shapes.rs
+++ b/render-wasm/src/shapes.rs
@@ -150,3 +150,21 @@ impl Shape {
         self.blend_mode = mode;
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn any_shape() -> Shape {
+        Shape::new(Uuid::nil())
+    }
+
+    #[test]
+    fn add_fill_pushes_a_new_fill() {
+        let mut shape = any_shape();
+        assert_eq!(shape.fills.len(), 0);
+
+        shape.add_fill(Fill::Solid(Color::TRANSPARENT));
+        assert_eq!(shape.fills.get(0), Some(&Fill::Solid(Color::TRANSPARENT)))
+    }
+}