Set metrics collector property before starting loop

Or we can get a message and cannot count it.

Author: acogoluegnes

src/main/java/com/rabbitmq/model/amqp/AmqpConsumer.java

@@ -77,8 +77,8 @@ class AmqpConsumer extends ResourceBase implements Consumer {
     this.nativeReceiver = createNativeReceiver(builder.connection().nativeSession(), this.address);
     this.initStateFromNativeReceiver(this.nativeReceiver);
     this.connection = builder.connection();
-    this.startReceivingLoop();
     this.metricsCollector = this.connection.metricsCollector();
+    this.startReceivingLoop();
     this.state(OPEN);
     this.metricsCollector.openConsumer();
   }

src/test/java/com/rabbitmq/model/amqp/MetricsCollectorTest.java

@@ -21,6 +21,7 @@
 import static com.rabbitmq.model.amqp.TestUtils.waitAtMost;
 import static com.rabbitmq.model.metrics.MetricsCollector.ConsumeDisposition.*;
 import static com.rabbitmq.model.metrics.MetricsCollector.PublishDisposition.FAILED;
+import static java.lang.String.format;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.*;
 
@@ -151,7 +152,9 @@ void metricsShouldBeCollected() throws Exception {
                     consumedCount.incrementAndGet();
                   })
               .build();
-      waitAtMost(() -> consumedCount.get() == 1);
+      waitAtMost(
+          () -> consumedCount.get() == 1,
+          () -> format("Expected 1 message, but got %d.", consumedCount.get()));
       // the first message is accepted
       verify(metricsCollector, times(1)).consume();
       verify(metricsCollector, times(1))