diff --git a/packages/mermaid/src/diagrams/state/stateDb.spec.js b/packages/mermaid/src/diagrams/state/stateDb.spec.js
new file mode 100644
index 000000000..786c122aa
--- /dev/null
+++ b/packages/mermaid/src/diagrams/state/stateDb.spec.js
@@ -0,0 +1,17 @@
+import stateDb from './stateDb';
+
+describe('stateDb', () => {
+  describe('addStyleClass', () => {
+    it('is added to the list of style classes', () => {
+      const newStyleClassId = 'newStyleClass';
+      const newStyleClassAttribs = 'font-weight:bold, border:blue;';
+
+      stateDb.addStyleClass(newStyleClassId, newStyleClassAttribs);
+      const styleClasses = stateDb.getClasses();
+      expect(styleClasses[newStyleClassId].id).toEqual(newStyleClassId);
+      expect(styleClasses[newStyleClassId].styles.length).toEqual(2);
+      expect(styleClasses[newStyleClassId].styles[0]).toEqual('font-weight:bold');
+      expect(styleClasses[newStyleClassId].styles[1]).toEqual('border:blue');
+    });
+  });
+});