Add data-mongo test for lazy loading collection like DBRef.

See: spring-projects/spring-data-mongodb#4351
See gh-176

data/data-mongodb/src/appTest/java/com/example/data/mongodb/DataMongoDbApplicationAotTests.java

@@ -47,6 +47,14 @@ class DataMongoDbApplicationAotTests {
 		});
 	}
 
+	@Test
+	void lazyDbRef(AssertableOutput output) {
+		Awaitility.await().atMost(Duration.ofSeconds(10)).untilAsserted(() -> {
+			assertThat(output).hasLineMatching(
+					".*List\\(\\d\\$LazyLoadingProxy\\)\\{\\W?com\\.example\\.data\\.mongodb\\.Coupon@.*\\W?\\}.*");
+		});
+	}
+
 	@Test
 	void queryByExample(AssertableOutput output) {
 		Awaitility.await().atMost(Duration.ofSeconds(10)).untilAsserted(() -> {

data/data-mongodb/src/main/java/com/example/data/mongodb/CLR.java

@@ -259,12 +259,15 @@ class CLR implements CommandLineRunner {
 		order.setCoupon(coupon);
 		order.setReduction(coupon);
 		order.setSimpleRef(coupon);
+		order.setAllCoupons(List.of(coupon));
 		orderRepository.save(order);
 
 		Optional<Order> loaded = orderRepository.findById(order.getId());
 		log("simple ref (no proxy): %s", loaded.get().getSimpleRef().getCode());
 		log("lazyLoading (aot): %s", loaded.get().getCoupon().getCode());
 		log("lazyLoading (jdk): %s", loaded.get().getReduction().getId());
+		log("lazyLoading - lists (jdk): List(%s){ %s }", loaded.get().getAllCoupons(),
+				loaded.get().getAllCoupons().get(0));
 
 		log("-----------------\n\n\n");
 	}

data/data-mongodb/src/main/java/com/example/data/mongodb/Order.java

@@ -59,6 +59,9 @@ public class Order {
 	@DBRef(lazy = true) // JdkProxy
 	private PriceReduction reduction;
 
+	@DBRef(lazy = true) // JdkProxy
+	private List<Coupon> allCoupons;
+
 	@DocumentReference
 	private Discount documentRef;
 
@@ -185,6 +188,14 @@ public class Order {
 		this.lazyDocumentRef = lazyDocumentRef;
 	}
 
+	public void setAllCoupons(List<Coupon> allCoupons) {
+		this.allCoupons = allCoupons;
+	}
+
+	public List<Coupon> getAllCoupons() {
+		return allCoupons;
+	}
+
 	@Override
 	public String toString() {
 		return "Order{" + "id='" + id + '\'' + ", customerId='" + customerId + '\'' + ", orderDate=" + orderDate