MINOR: Implement toString method for TopicAssignment and PartitionAssignment (#13101)

Implements `toString` method for classes `TopicAssignment` and` PartitionAssignment`. Also removes the `final` keyword from the constructor arguments for consistency.

Reviewers: José Armando García Sancio <jsancio@apache.org>

metadata/src/main/java/org/apache/kafka/metadata/placement/PartitionAssignment.java

@@ -31,7 +31,7 @@ import java.util.Objects;
 public class PartitionAssignment {
     private final List<Integer> replicas;
 
-    public PartitionAssignment(final List<Integer> replicas) {
+    public PartitionAssignment(List<Integer> replicas) {
         this.replicas = Collections.unmodifiableList(new ArrayList<>(replicas));
     }
 
@@ -53,4 +53,11 @@ public class PartitionAssignment {
     public int hashCode() {
         return Objects.hash(replicas);
     }
+
+    @Override
+    public String toString() {
+        return "PartitionAssignment" +
+            "(replicas=" + replicas +
+            ")";
+    }
 }

metadata/src/main/java/org/apache/kafka/metadata/placement/TopicAssignment.java

@@ -30,7 +30,7 @@ import java.util.Objects;
 public class TopicAssignment {
     private final List<PartitionAssignment> assignments;
 
-    public TopicAssignment(final List<PartitionAssignment> assignments) {
+    public TopicAssignment(List<PartitionAssignment> assignments) {
         this.assignments = Collections.unmodifiableList(new ArrayList<>(assignments));
     }
 
@@ -52,4 +52,11 @@ public class TopicAssignment {
     public int hashCode() {
         return Objects.hash(assignments);
     }
+
+    @Override
+    public String toString() {
+        return "TopicAssignment" +
+            "(assignments=" + assignments +
+            ")";
+    }
 }

metadata/src/test/java/org/apache/kafka/metadata/placement/PartitionAssignmentTest.java

@@ -57,4 +57,11 @@ public class PartitionAssignmentTest {
             }
         }
     }
+
+    @Test
+    public void testToString() {
+        List<Integer> replicas = Arrays.asList(0, 1, 2);
+        PartitionAssignment partitionAssignment = new PartitionAssignment(replicas);
+        assertEquals("PartitionAssignment(replicas=[0, 1, 2])", partitionAssignment.toString());
+    }
 }

metadata/src/test/java/org/apache/kafka/metadata/placement/TopicAssignmentTest.java

@@ -33,7 +33,7 @@ public class TopicAssignmentTest {
         List<Integer> replicasP1 = Arrays.asList(1, 2, 0);
         List<PartitionAssignment> partitionAssignments = Arrays.asList(
             new PartitionAssignment(replicasP0),
-             new PartitionAssignment(replicasP1)
+            new PartitionAssignment(replicasP1)
         );
         assertEquals(partitionAssignments, new TopicAssignment(partitionAssignments).assignments());
     }
@@ -53,7 +53,7 @@ public class TopicAssignmentTest {
                     new PartitionAssignment(
                         Arrays.asList(1, 2, 0)
                     )
-                 )
+                )
             )
         );
 
@@ -70,4 +70,14 @@ public class TopicAssignmentTest {
             }
         }
     }
+
+    @Test
+    public void testToString() {
+        List<Integer> replicas = Arrays.asList(0, 1, 2);
+        List<PartitionAssignment> partitionAssignments = Arrays.asList(
+            new PartitionAssignment(replicas)
+        );
+        TopicAssignment topicAssignment = new TopicAssignment(partitionAssignments);
+        assertEquals("TopicAssignment(assignments=[PartitionAssignment(replicas=[0, 1, 2])])", topicAssignment.toString());
+    }
 }