LOG4J2-1689 Adding unit test

log4j-api/src/test/java/org/apache/logging/log4j/ThreadContextTest.java

@@ -16,6 +16,7 @@
  */
 package org.apache.logging.log4j;
 
+import java.util.Arrays;
 import java.util.HashMap;
 import java.util.Map;
 
@@ -182,6 +183,21 @@ public class ThreadContextTest {
         assertTrue(ThreadContext.isEmpty());
     }
 
+    @Test
+    public void testRemoveAll() {
+        ThreadContext.clearMap();
+        ThreadContext.put("testKey1", "testValue1");
+        ThreadContext.put("testKey2", "testValue2");
+        assertEquals("testValue1", ThreadContext.get("testKey1"));
+        assertEquals("testValue2", ThreadContext.get("testKey2"));
+        assertFalse(ThreadContext.isEmpty());
+
+        ThreadContext.removeAll(Arrays.asList("testKey1", "testKey2"));
+        assertNull(ThreadContext.get("testKey1"));
+        assertNull(ThreadContext.get("testKey2"));
+        assertTrue(ThreadContext.isEmpty());
+    }
+
     @Test
     public void testContainsKey() {
         ThreadContext.clearMap();