Polish MessageHeaderAccessor

Issue: SPR-12431

spring-messaging/src/test/java/org/springframework/messaging/support/MessageHeaderAccessorTests.java

@@ -39,6 +39,7 @@ import static org.junit.Assert.*;
  * Test fixture for {@link MessageHeaderAccessor}.
  *
  * @author Rossen Stoyanchev
+ * @author Sebastien Deleuze
  */
 public class MessageHeaderAccessorTests {
 
@@ -88,6 +89,58 @@ public class MessageHeaderAccessorTests {
 		assertEquals("baz", actual.get("bar"));
 	}
 
+	@Test
+	public void removeHeaders() {
+		Map<String, Object> map = new HashMap<>();
+		map.put("foo", "bar");
+		map.put("bar", "baz");
+		GenericMessage<String> message = new GenericMessage<>("payload", map);
+		MessageHeaderAccessor accessor = new MessageHeaderAccessor(message);
+
+		accessor.removeHeaders("fo*");
+
+		MessageHeaders actual = accessor.getMessageHeaders();
+		assertEquals(2, actual.size());
+		assertNull(actual.get("foo"));
+		assertEquals("baz", actual.get("bar"));
+	}
+
+	@Test
+	public void copyHeaders() {
+		Map<String, Object> map1 = new HashMap<>();
+		map1.put("foo", "bar");
+		GenericMessage<String> message = new GenericMessage<>("payload", map1);
+		MessageHeaderAccessor accessor = new MessageHeaderAccessor(message);
+
+		Map<String, Object> map2 = new HashMap<>();
+		map2.put("foo", "BAR");
+		map2.put("bar", "baz");
+		accessor.copyHeaders(map2);
+
+		MessageHeaders actual = accessor.getMessageHeaders();
+		assertEquals(3, actual.size());
+		assertEquals("BAR", actual.get("foo"));
+		assertEquals("baz", actual.get("bar"));
+	}
+
+	@Test
+	public void copyHeadersIfAbsent() {
+		Map<String, Object> map1 = new HashMap<>();
+		map1.put("foo", "bar");
+		GenericMessage<String> message = new GenericMessage<>("payload", map1);
+		MessageHeaderAccessor accessor = new MessageHeaderAccessor(message);
+
+		Map<String, Object> map2 = new HashMap<>();
+		map2.put("foo", "BAR");
+		map2.put("bar", "baz");
+		accessor.copyHeadersIfAbsent(map2);
+
+		MessageHeaders actual = accessor.getMessageHeaders();
+		assertEquals(3, actual.size());
+		assertEquals("bar", actual.get("foo"));
+		assertEquals("baz", actual.get("bar"));
+	}
+
 	@Test
 	public void copyHeadersFromNullMap() {
 		MessageHeaderAccessor headers = new MessageHeaderAccessor();