diff --git a/src/test/java/org/apache/commons/collections4/map/MultiKeyMapTest.java b/src/test/java/org/apache/commons/collections4/map/MultiKeyMapTest.java
index 9c5238b3e5..c532dba3cf 100644
--- a/src/test/java/org/apache/commons/collections4/map/MultiKeyMapTest.java
+++ b/src/test/java/org/apache/commons/collections4/map/MultiKeyMapTest.java
@@ -489,6 +489,45 @@ void testMultiKeyRemoveAll4() {
         }
     }
 
+    @Test
+    void testClassCastExceptionOnNonMultiKey() {
+        final MultiKeyMap<String, String> map = new MultiKeyMap<>();
+        final Object nonMultiKey = "test";
+        assertThrows(ClassCastException.class, () -> map.put((MultiKey<? extends String>) nonMultiKey, "value"));
+    }
+
+    @Test
+    void testMultiKeyMapNullMap() {
+        assertThrows(NullPointerException.class, () -> MultiKeyMap.multiKeyMap(null));
+    }
+
+    @Test
+    void testMultiKeyRemoveAll_ReturnsTrueWhenEntriesRemoved() {
+        resetFull();
+        final MultiKeyMap<K, V> multimap = getMap();
+        assertEquals(12, multimap.size());
+
+        final boolean result = multimap.removeAll(I1);
+        assertEquals(8, multimap.size());
+        assertTrue(result);
+
+        for (final MapIterator<MultiKey<? extends K>, V> it = multimap.mapIterator(); it.hasNext();) {
+            final MultiKey<? extends K> key = it.next();
+            assertFalse(I1.equals(key.getKey(0)));
+        }
+    }
+
+    @Test
+    void testMultiKeyRemoveAll_ReturnsFalseWhenNoEntriesRemoved() {
+        resetFull();
+        final MultiKeyMap<K, V> multimap = getMap();
+        assertEquals(12, multimap.size());
+
+        final boolean result = multimap.removeAll(new Object());
+        assertEquals(12, multimap.size());
+        assertFalse(result);
+    }
+
     @Test
     @SuppressWarnings("unchecked")
     void testNullHandling() {
diff --git a/src/test/java/org/apache/commons/collections4/queue/CircularFifoQueueTest.java b/src/test/java/org/apache/commons/collections4/queue/CircularFifoQueueTest.java
index 35340d6e27..b477bb4407 100644
--- a/src/test/java/org/apache/commons/collections4/queue/CircularFifoQueueTest.java
+++ b/src/test/java/org/apache/commons/collections4/queue/CircularFifoQueueTest.java
@@ -451,6 +451,26 @@ void testRepeatedSerialization() throws Exception {
 //        writeExternalFormToDisk((java.io.Serializable) getCollection(), "src/test/resources/data/test/CircularFifoQueue.fullCollection.version4.obj");
 //    }
 
+    @Test
+    void testAddAlwaysReturnsTrue() {
+        final CircularFifoQueue<E> queue = new CircularFifoQueue<>(3);
+        queue.add((E) "1");
+        queue.add((E) "2");
+        queue.add((E) "3");
+        assertTrue(queue.add((E) "4"));
+        assertTrue(queue.add((E) "5"));
+    }
+
+    @Test
+    void testIsEmpty() {
+        final CircularFifoQueue<String> queue = new CircularFifoQueue<>(10);
+        assertTrue(queue.isEmpty());
+        queue.add("test");
+        assertFalse(queue.isEmpty());
+        queue.remove("test");
+        assertTrue(queue.isEmpty());
+    }
+
     /**
      *  Runs through the regular verifications, but also verifies that
      *  the buffer contains the same elements in the same sequence as the