diff --git a/__tests__/service-worker/service-worker.test.js b/__tests__/service-worker/service-worker.test.js
index 43c9601..9aa522a 100644
--- a/__tests__/service-worker/service-worker.test.js
+++ b/__tests__/service-worker/service-worker.test.js
@@ -232,9 +232,9 @@ beforeAll(async ()=>{
                 postMessage: window.clients.prototypePostMessage
             }
         },
-        claim: async () => {
+        claim: spy(async () => {
             return undefined
-        },
+        }),
         // the actual spy function must be possible to reference
         // but we want spy data per test, so we set it properly in beforeEach()
         prototypePostMessage: null
@@ -443,6 +443,14 @@ describe('service-worker', async () => {
     
     window.test_id = 0
     
+    it("should call clients.claim() when activated", async () => {
+        await import("../../service-worker.js?" + window.test_id);
+        await self.dispatchEvent(new Event('install'))
+        await self.waitForSWInstall()
+        await self.dispatchEvent(new Event('activate'))
+        assertSpyCalls(window.clients.claim, 1)
+    })
+    
     it("should use default LibResilientConfig values when config.json is missing", async () => {
         
         let mock_response_data = {