diff --git a/junit/kubernetes-server-mock/src/test/java/io/fabric8/kubernetes/client/server/mock/crud/KubernetesCrudDispatcherPatchTest.java b/junit/kubernetes-server-mock/src/test/java/io/fabric8/kubernetes/client/server/mock/crud/KubernetesCrudDispatcherPatchTest.java
index 9933708a6b5..21bd983f6f7 100644
--- a/junit/kubernetes-server-mock/src/test/java/io/fabric8/kubernetes/client/server/mock/crud/KubernetesCrudDispatcherPatchTest.java
+++ b/junit/kubernetes-server-mock/src/test/java/io/fabric8/kubernetes/client/server/mock/crud/KubernetesCrudDispatcherPatchTest.java
@@ -36,6 +36,7 @@
 import java.util.function.UnaryOperator;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
@@ -319,11 +320,10 @@ void differentResourceVersionConflictEdit() {
           .addToData("key", "changed")
           .build());
       // Then
-      assertThatThrownBy(patchedCmOp::patch)
-          .asInstanceOf(InstanceOfAssertFactories.type(KubernetesClientException.class))
+      assertThatExceptionOfType(KubernetesClientException.class)
+          .isThrownBy(patchedCmOp::patch)
           .hasFieldOrPropertyWithValue("code", 409)
-          .extracting(KubernetesClientException::getMessage).asString()
-          .contains("the object has been modified;");
+          .withMessageContaining("the object has been modified;");
     }
 
     @Test
diff --git a/junit/mockwebserver/src/test/groovy/io/fabric8/mockwebserver/DefaultMockServerTest.groovy b/junit/mockwebserver/src/test/groovy/io/fabric8/mockwebserver/DefaultMockServerTest.groovy
index 85a6d9ca769..5ff230abda4 100644
--- a/junit/mockwebserver/src/test/groovy/io/fabric8/mockwebserver/DefaultMockServerTest.groovy
+++ b/junit/mockwebserver/src/test/groovy/io/fabric8/mockwebserver/DefaultMockServerTest.groovy
@@ -620,7 +620,7 @@ class DefaultMockServerTest extends Specification {
       server.expect().get().withPath("/api/v1/users/watch")
         .andUpgradeToWebSocket()
         .open()
-        .immediately().andEmit("READY")
+        .waitFor(50L).andEmit("READY")
         .expectHttpRequest("/api/v1/create").andEmit("CREATED").once()
         .expectSentWebSocketMessage("CREATED").andEmit("WS-CREATED").once()
         .done()
diff --git a/junit/mockwebserver/src/test/groovy/io/fabric8/mockwebserver/DefaultMockServerWebSocketTest.groovy b/junit/mockwebserver/src/test/groovy/io/fabric8/mockwebserver/DefaultMockServerWebSocketTest.groovy
index ac596b9cefe..41989c6ca69 100644
--- a/junit/mockwebserver/src/test/groovy/io/fabric8/mockwebserver/DefaultMockServerWebSocketTest.groovy
+++ b/junit/mockwebserver/src/test/groovy/io/fabric8/mockwebserver/DefaultMockServerWebSocketTest.groovy
@@ -123,9 +123,13 @@ class DefaultMockServerWebSocketTest extends Specification {
       def wsReq = wsClient.webSocket().connect(server.port, server.getHostName(), "/websocket")
     and: "A WebSocket listener"
       wsReq.onComplete { ws ->
-        ws.result().closeHandler { _ ->
-          ws.result().close()
+        if (ws.result().isClosed()) {
           future.complete(ws.result().closeReason())
+        } else {
+          ws.result().closeHandler { _ ->
+            ws.result().close()
+            future.complete(ws.result().closeReason())
+          }
         }
       }
     and: "An instance of AsyncConditions"
diff --git a/kubernetes-client-api/src/test/java/io/fabric8/kubernetes/client/http/StandardHttpClientTest.java b/kubernetes-client-api/src/test/java/io/fabric8/kubernetes/client/http/StandardHttpClientTest.java
index f3664e9e9d4..feefd0a4b5c 100644
--- a/kubernetes-client-api/src/test/java/io/fabric8/kubernetes/client/http/StandardHttpClientTest.java
+++ b/kubernetes-client-api/src/test/java/io/fabric8/kubernetes/client/http/StandardHttpClientTest.java
@@ -41,6 +41,7 @@
 import java.util.stream.Stream;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 import static org.assertj.core.api.Assertions.assertThatThrownBy;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -231,8 +232,9 @@ void testRequestTimeout() {
         });
 
     Awaitility.await().atMost(10, TimeUnit.SECONDS).until(consumeFuture::isDone);
-    assertThatThrownBy(consumeFuture::get)
-        .isInstanceOf(ExecutionException.class).hasCauseInstanceOf(TimeoutException.class);
+    assertThatExceptionOfType(ExecutionException.class)
+        .isThrownBy(consumeFuture::get)
+        .withCauseExactlyInstanceOf(TimeoutException.class);
   }
 
   @Test
diff --git a/pom.xml b/pom.xml
index 929306b1011..98b141e50f0 100644
--- a/pom.xml
+++ b/pom.xml
@@ -109,7 +109,7 @@
 
     <!-- Testing versions -->
     <junit.version>5.10.1</junit.version>
-    <assertj.core.version>3.24.2</assertj.core.version>
+    <assertj.core.version>3.25.0</assertj.core.version>
     <awaitility.version>4.2.0</awaitility.version>
     <approvaltests.version>22.3.3</approvaltests.version>
     <mockito.version>4.11.0</mockito.version>