diff --git a/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/FeignBuilderCustomizerTests.java b/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/FeignBuilderCustomizerTests.java
index 4b728d58..f93c7c36 100644
--- a/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/FeignBuilderCustomizerTests.java
+++ b/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/FeignBuilderCustomizerTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2022 the original author or authors.
+ * Copyright 2013-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -22,7 +22,6 @@ import java.util.stream.Stream;
 import feign.Client;
 import feign.Feign;
 import feign.Logger;
-import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.MethodSource;
@@ -65,7 +64,7 @@ class FeignBuilderCustomizerTests {
 		FeignClientFactoryBean clientFactoryBean = context.getBean(FeignClientFactoryBean.class);
 		clientFactoryBean.getTarget();
 
-		Assertions.assertNotNull(feignBuilderCaptor.getValue());
+		assertThat(feignBuilderCaptor.getValue()).isNotNull();
 		Feign.Builder builder = feignBuilderCaptor.getValue();
 		assertFeignBuilderField(builder, "logLevel", Logger.Level.HEADERS);
 		assertFeignBuilderField(builder, "dismiss404", true);
@@ -92,7 +91,7 @@ class FeignBuilderCustomizerTests {
 		FeignClientFactoryBean clientFactoryBean = context.getBean(FeignClientFactoryBean.class);
 		clientFactoryBean.getTarget();
 
-		Assertions.assertNotNull(feignBuilderCaptor.getValue());
+		assertThat(feignBuilderCaptor.getValue()).isNotNull();
 		Feign.Builder builder = feignBuilderCaptor.getValue();
 		assertFeignBuilderField(builder, "logLevel", Logger.Level.FULL);
 		assertFeignBuilderField(builder, "dismiss404", true);
@@ -113,7 +112,7 @@ class FeignBuilderCustomizerTests {
 		clientFactoryBean.addCustomizer(Feign.Builder::doNotCloseAfterDecode);
 		clientFactoryBean.getTarget();
 
-		Assertions.assertNotNull(feignBuilderCaptor.getValue());
+		assertThat(feignBuilderCaptor.getValue()).isNotNull();
 		Feign.Builder builder = feignBuilderCaptor.getValue();
 		assertFeignBuilderField(builder, "logLevel", Logger.Level.BASIC);
 		assertFeignBuilderField(builder, "dismiss404", true);
@@ -134,7 +133,7 @@ class FeignBuilderCustomizerTests {
 		clientFactoryBean.addCustomizer(builder -> builder.client(customClientMock));
 		clientFactoryBean.getTarget();
 
-		Assertions.assertNotNull(feignBuilderCaptor.getValue());
+		assertThat(feignBuilderCaptor.getValue()).isNotNull();
 		Feign.Builder builder = feignBuilderCaptor.getValue();
 		assertFeignBuilderField(builder, "client", customClientMock);
 
diff --git a/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/support/AbstractFormWriterTests.java b/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/support/FormWriterTests.java
similarity index 74%
rename from spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/support/AbstractFormWriterTests.java
rename to spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/support/FormWriterTests.java
index 4786298e..fd9a8543 100644
--- a/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/support/AbstractFormWriterTests.java
+++ b/spring-cloud-openfeign-core/src/test/java/org/springframework/cloud/openfeign/support/FormWriterTests.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2013-2022 the original author or authors.
+ * Copyright 2013-2025 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,29 +16,31 @@
 
 package org.springframework.cloud.openfeign.support;
 
-import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.http.MediaType;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 /**
  * @author Wu Daifu
+ * @author Olga Maciaszek-Sharma
  */
-class AbstractFormWriterTests {
+class FormWriterTests {
 
 	@Test
 	void shouldCorrectlyResolveIfApplicableForCollection() {
 		MockFormWriter formWriter = new MockFormWriter();
 		Object object = new Object();
-		Assertions.assertFalse(formWriter.isApplicable(object));
+		assertThat(formWriter.isApplicable(object)).isFalse();
 		object = new Object[] { new Object(), new Object() };
-		Assertions.assertFalse(formWriter.isApplicable(object));
+		assertThat(formWriter.isApplicable(object)).isFalse();
 		object = new UserPojo();
-		Assertions.assertTrue(formWriter.isApplicable(object));
+		assertThat(formWriter.isApplicable(object)).isTrue();
 		object = new UserPojo[] { new UserPojo(), new UserPojo() };
-		Assertions.assertTrue(formWriter.isApplicable(object));
+		assertThat(formWriter.isApplicable(object)).isTrue();
 		object = new byte[] { '1', '2' };
-		Assertions.assertFalse(formWriter.isApplicable(object));
+		assertThat(formWriter.isApplicable(object)).isFalse();
 	}
 
 	static class MockFormWriter extends AbstractFormWriter {