diff --git a/core/src/test/java/org/apache/commons/proxy2/interceptor/InvokerInterceptorTest.java b/core/src/test/java/org/apache/commons/proxy2/interceptor/InvokerInterceptorTest.java
index 6fea1f0..65a578b 100644
--- a/core/src/test/java/org/apache/commons/proxy2/interceptor/InvokerInterceptorTest.java
+++ b/core/src/test/java/org/apache/commons/proxy2/interceptor/InvokerInterceptorTest.java
@@ -18,6 +18,7 @@
 package org.apache.commons.proxy2.interceptor;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
 
 import java.lang.reflect.Method;
 
@@ -55,6 +56,6 @@
     @Test(expected = NullPointerException.class)
     public void testWithNullInvoker()
     {
-        new InvokerInterceptor(null);
+        assertNotNull(new InvokerInterceptor(null)); // assert is used to avoid not used warning
     }
 }
diff --git a/core/src/test/java/org/apache/commons/proxy2/interceptor/ObjectProviderInterceptorTest.java b/core/src/test/java/org/apache/commons/proxy2/interceptor/ObjectProviderInterceptorTest.java
index 69b4467..c4ef064 100644
--- a/core/src/test/java/org/apache/commons/proxy2/interceptor/ObjectProviderInterceptorTest.java
+++ b/core/src/test/java/org/apache/commons/proxy2/interceptor/ObjectProviderInterceptorTest.java
@@ -18,6 +18,7 @@
 package org.apache.commons.proxy2.interceptor;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
 
 import org.apache.commons.proxy2.provider.ObjectProviderUtils;
 import org.apache.commons.proxy2.util.AbstractTestCase;
@@ -39,6 +40,6 @@
     @Test(expected = NullPointerException.class)
     public void testWithNullProvider()
     {
-        new ObjectProviderInterceptor(null);
+        assertNotNull(new ObjectProviderInterceptor(null)); // assert is used to avoid not used warning
     }
 }
diff --git a/core/src/test/java/org/apache/commons/proxy2/provider/CloningProviderTest.java b/core/src/test/java/org/apache/commons/proxy2/provider/CloningProviderTest.java
index e160fa0..c320dc7 100644
--- a/core/src/test/java/org/apache/commons/proxy2/provider/CloningProviderTest.java
+++ b/core/src/test/java/org/apache/commons/proxy2/provider/CloningProviderTest.java
@@ -18,6 +18,7 @@
 package org.apache.commons.proxy2.provider;
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNotSame;
 import static org.junit.Assert.fail;
 
@@ -71,7 +72,7 @@
     @Test(expected = IllegalArgumentException.class)
     public void testWithInvalidCloneable()
     {
-        new CloningProvider<InvalidCloneable>(new InvalidCloneable());
+        assertNotNull(new CloningProvider<InvalidCloneable>(new InvalidCloneable())); // assert is used to avoid not used warning
     }
 
     @Test(expected = IllegalArgumentException.class)