Minor refactorings and code style changes (#807)

* Made minor changes in some patterns such as removed throws clause where not needed, changed incorrect order of arguments in assertEquals

* Minor refactorings and code style changes. 1) Removed several use of raw types 2) Removed unnecessary throws clauses 3) Used lambda expressions wherever applicable 4) Used apt assertion methods for readability 5) Use of try with resources wherever applicable 6) Corrected incorrect order of assertXXX arguments

* Removed unused import from Promise

* Addressed review comments

* Addressed checkstyle issue

poison-pill/src/test/java/com/iluwatar/poison/pill/PoisonMessageTest.java

@@ -36,38 +36,34 @@ import static org.junit.jupiter.api.Assertions.assertThrows;
 public class PoisonMessageTest {
 
   @Test
-  public void testAddHeader() throws Exception {
+  public void testAddHeader() {
     assertThrows(UnsupportedOperationException.class, () -> {
       POISON_PILL.addHeader(Headers.SENDER, "sender");
     });
   }
 
   @Test
-  public void testGetHeader() throws Exception {
+  public void testGetHeader() {
     assertThrows(UnsupportedOperationException.class, () -> {
       POISON_PILL.getHeader(Headers.SENDER);
     });
   }
 
   @Test
-  public void testGetHeaders() throws Exception {
-    assertThrows(UnsupportedOperationException.class, () -> {
-      POISON_PILL.getHeaders();
-    });
+  public void testGetHeaders() {
+    assertThrows(UnsupportedOperationException.class, POISON_PILL::getHeaders);
   }
 
   @Test
-  public void testSetBody() throws Exception {
+  public void testSetBody() {
     assertThrows(UnsupportedOperationException.class, () -> {
       POISON_PILL.setBody("Test message.");
     });
   }
 
   @Test
-  public void testGetBody() throws Exception {
-    assertThrows(UnsupportedOperationException.class, () -> {
-      POISON_PILL.getBody();
-    });
+  public void testGetBody() {
+    assertThrows(UnsupportedOperationException.class, POISON_PILL::getBody);
   }
 
 }