diff --git a/src/test/java/org/apache/commons/collections4/CollectionUtilsTest.java b/src/test/java/org/apache/commons/collections4/CollectionUtilsTest.java
index 9f5e2010b..4ce267cd7 100644
--- a/src/test/java/org/apache/commons/collections4/CollectionUtilsTest.java
+++ b/src/test/java/org/apache/commons/collections4/CollectionUtilsTest.java
@@ -1229,7 +1229,7 @@ public class CollectionUtilsTest extends MockTestCase {
 
         final List<Integer> combinedList = new ArrayList<>(collectionD);
         combinedList.addAll(collectionE);
-        Collections.sort(combinedList);
+        combinedList.sort(null);
 
         assertEquals(combinedList, result2, "Merge two lists 2");
 
@@ -1258,7 +1258,7 @@ public class CollectionUtilsTest extends MockTestCase {
         final Set<Integer> combinedSet = new HashSet<>(collectionD);
         combinedSet.addAll(collectionE);
         final List<Integer> combinedList = new ArrayList<>(combinedSet);
-        Collections.sort(combinedList);
+        combinedList.sort(null);
 
         assertEquals(combinedList, result2, "Merge two lists 2 - ignore duplicates");
     }
diff --git a/src/test/java/org/apache/commons/collections4/FluentIterableTest.java b/src/test/java/org/apache/commons/collections4/FluentIterableTest.java
index 9e9b2f7dc..492044a0c 100644
--- a/src/test/java/org/apache/commons/collections4/FluentIterableTest.java
+++ b/src/test/java/org/apache/commons/collections4/FluentIterableTest.java
@@ -161,7 +161,7 @@ public class FluentIterableTest {
         final List<Integer> combinedList = new ArrayList<>();
         CollectionUtils.addAll(combinedList, iterableOdd);
         CollectionUtils.addAll(combinedList, iterableEven);
-        Collections.sort(combinedList);
+        combinedList.sort(null);
         assertEquals(combinedList, result);
 
         try {
@@ -183,7 +183,7 @@ public class FluentIterableTest {
         final List<Integer> combinedList = new ArrayList<>();
         CollectionUtils.addAll(combinedList, iterableOdd);
         CollectionUtils.addAll(combinedList, iterableEven);
-        Collections.sort(combinedList);
+        combinedList.sort(null);
         assertEquals(combinedList, result);
 
         // null comparator is equivalent to natural ordering
@@ -352,7 +352,7 @@ public class FluentIterableTest {
         List<Integer> combinedList = new ArrayList<>();
         CollectionUtils.addAll(combinedList, iterableOdd);
         CollectionUtils.addAll(combinedList, iterableEven);
-        Collections.sort(combinedList);
+        combinedList.sort(null);
         assertEquals(combinedList, result);
 
         try {
diff --git a/src/test/java/org/apache/commons/collections4/IteratorUtilsTest.java b/src/test/java/org/apache/commons/collections4/IteratorUtilsTest.java
index 71294e58b..f2c88f7a8 100644
--- a/src/test/java/org/apache/commons/collections4/IteratorUtilsTest.java
+++ b/src/test/java/org/apache/commons/collections4/IteratorUtilsTest.java
@@ -579,7 +579,7 @@ public class IteratorUtilsTest {
 
         final List<Integer> combinedList = new ArrayList<>(collectionOdd);
         combinedList.addAll(collectionEven);
-        Collections.sort(combinedList);
+        combinedList.sort(null);
 
         assertEquals(combinedList, result);
 
diff --git a/src/test/java/org/apache/commons/collections4/bidimap/AbstractSortedBidiMapTest.java b/src/test/java/org/apache/commons/collections4/bidimap/AbstractSortedBidiMapTest.java
index 87d7663c9..6532cde75 100644
--- a/src/test/java/org/apache/commons/collections4/bidimap/AbstractSortedBidiMapTest.java
+++ b/src/test/java/org/apache/commons/collections4/bidimap/AbstractSortedBidiMapTest.java
@@ -44,7 +44,7 @@ public abstract class AbstractSortedBidiMapTest<K extends Comparable<K>, V exten
     public AbstractSortedBidiMapTest(final String testName) {
         super(testName);
         sortedKeys = getAsList(getSampleKeys());
-        Collections.sort(sortedKeys);
+        sortedKeys.sort(null);
         sortedKeys = Collections.unmodifiableList(sortedKeys);
 
         final Map<K, V> map = new TreeMap<>();
diff --git a/src/test/java/org/apache/commons/collections4/bidimap/DualTreeBidiMap2Test.java b/src/test/java/org/apache/commons/collections4/bidimap/DualTreeBidiMap2Test.java
index b52cf2dbb..8134d7d9a 100644
--- a/src/test/java/org/apache/commons/collections4/bidimap/DualTreeBidiMap2Test.java
+++ b/src/test/java/org/apache/commons/collections4/bidimap/DualTreeBidiMap2Test.java
@@ -129,7 +129,7 @@ public class DualTreeBidiMap2Test<K extends Comparable<K>, V extends Comparable<
 
         // Sort by the comparator used in the makeEmptyBidiMap() method
         List<K> newSortedKeys = getAsList(getSampleKeys());
-        Collections.sort(newSortedKeys, new ReverseComparator<>(ComparableComparator.<K>comparableComparator()));
+        newSortedKeys.sort(new ReverseComparator<>(ComparableComparator.<K>comparableComparator()));
         newSortedKeys = Collections.unmodifiableList(newSortedKeys);
 
         final Iterator<K> mapIter = sm.keySet().iterator();
diff --git a/src/test/java/org/apache/commons/collections4/junit/AbstractAvailableLocalesTest.java b/src/test/java/org/apache/commons/collections4/junit/AbstractAvailableLocalesTest.java
index 4254bcc21..32a73efc1 100644
--- a/src/test/java/org/apache/commons/collections4/junit/AbstractAvailableLocalesTest.java
+++ b/src/test/java/org/apache/commons/collections4/junit/AbstractAvailableLocalesTest.java
@@ -74,7 +74,7 @@ public abstract class AbstractAvailableLocalesTest {
                 }
             }
         }
-        Collections.sort(availableLocales, new ObjectToStringComparator());
+        availableLocales.sort(ObjectToStringComparator.INSTANCE);
         return availableLocales;
     }
 
diff --git a/src/test/java/org/apache/commons/collections4/junit/ObjectToStringComparator.java b/src/test/java/org/apache/commons/collections4/junit/ObjectToStringComparator.java
index eee8ed801..e36736704 100644
--- a/src/test/java/org/apache/commons/collections4/junit/ObjectToStringComparator.java
+++ b/src/test/java/org/apache/commons/collections4/junit/ObjectToStringComparator.java
@@ -27,7 +27,7 @@ public final class ObjectToStringComparator implements Comparator<Object>, Seria
      *
      * @since 4.5
      */
-    public final ObjectToStringComparator INSTANCE = new ObjectToStringComparator();
+    public static final ObjectToStringComparator INSTANCE = new ObjectToStringComparator();
 
     private static final long serialVersionUID = 1L;
 
diff --git a/src/test/java/org/apache/commons/collections4/map/AbstractOrderedMapTest.java b/src/test/java/org/apache/commons/collections4/map/AbstractOrderedMapTest.java
index 17ff23683..aa7eee1f9 100644
--- a/src/test/java/org/apache/commons/collections4/map/AbstractOrderedMapTest.java
+++ b/src/test/java/org/apache/commons/collections4/map/AbstractOrderedMapTest.java
@@ -78,7 +78,7 @@ public abstract class AbstractOrderedMapTest<K, V> extends AbstractIterableMapTe
     @SuppressWarnings("unchecked")
     public K[] getSampleKeys() {
         final List<K> list = new ArrayList<>(Arrays.asList(super.getSampleKeys()));
-        Collections.sort(list, new NullComparator<K>());
+        list.sort(new NullComparator<K>());
         return (K[]) list.toArray();
     }