added tests to ensure MongoCursor is closed

mongo/pom.xml

@@ -84,6 +84,12 @@
       <version>1.7.25</version>
       <scope>test</scope>
     </dependency>
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-core</artifactId>
+      <version>1.10.19</version>
+      <scope>test</scope>
+    </dependency>
   </dependencies>
   <profiles>
     <profile>

mongo/src/org/immutables/mongo/repository/Repositories.java

@@ -24,6 +24,7 @@
 import com.google.gson.TypeAdapter;
 import com.mongodb.client.FindIterable;
 import com.mongodb.client.MongoCollection;
+import com.mongodb.client.MongoCursor;
 import com.mongodb.client.model.FindOneAndDeleteOptions;
 import com.mongodb.client.model.FindOneAndReplaceOptions;
 import com.mongodb.client.model.FindOneAndUpdateOptions;
@@ -319,7 +320,10 @@ public List<T> call() throws Exception {
             }
           }
 
-          return ImmutableList.copyOf(cursor);
+          // close properly
+          try (MongoCursor<T> iterator = cursor.iterator()) {
+            return ImmutableList.copyOf(iterator);
+          }
         }
       });
     }

mongo/test/org/immutables/mongo/fixture/MongoCursorIsClosedTest.java

@@ -0,0 +1,93 @@
+package org.immutables.mongo.fixture;
+
+import com.google.common.util.concurrent.MoreExecutors;
+import com.google.gson.GsonBuilder;
+import com.mongodb.client.FindIterable;
+import com.mongodb.client.MongoCollection;
+import com.mongodb.client.MongoCursor;
+import com.mongodb.client.MongoDatabase;
+import org.bson.codecs.configuration.CodecRegistry;
+import org.bson.conversions.Bson;
+import org.immutables.mongo.repository.RepositorySetup;
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.immutables.check.Checkers.check;
+import static org.junit.Assert.fail;
+import static org.mockito.Matchers.any;
+import static org.mockito.Matchers.anyString;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+/**
+ * Set of tests to ensure mongo resources are properly closed.
+ *
+ * @see MongoCursor#close()
+ * @see <a href="https://docs.mongodb.com/v3.4/reference/method/cursor.close/">cursor.close</a>
+ */
+public class MongoCursorIsClosedTest {
+
+  private EntityRepository repository;
+
+  private MongoCursor<Entity> cursor;
+
+  @Before
+  @SuppressWarnings("unchecked")
+  public void setUp() throws Exception {
+    MongoDatabase db = mock(MongoDatabase.class);
+    MongoCollection collection = mock(MongoCollection.class);
+
+    when(db.getCollection(anyString())).thenReturn(collection);
+    when(collection.withDocumentClass(any(Class.class))).thenReturn(collection);
+    when(collection.withCodecRegistry(any(CodecRegistry.class))).thenReturn(collection);
+
+    RepositorySetup setup = RepositorySetup.builder().database(db)
+            .executor(MoreExecutors.newDirectExecutorService())
+            .gson(new GsonBuilder().registerTypeAdapterFactory(new GsonAdaptersEntity()).create())
+            .build();
+
+    this.repository = new EntityRepository(setup);
+
+    FindIterable<Entity> iterable = mock(FindIterable.class);
+    when(collection.find(any(Bson.class))).thenReturn(iterable);
+    MongoCursor<Entity> cursor = mock(MongoCursor.class);
+    when(iterable.iterator()).thenReturn(cursor);
+
+    this.cursor = cursor;
+  }
+
+  @Test
+  public void emptyResult() throws Exception {
+    when(cursor.hasNext()).thenReturn(false);
+    check(repository.findAll().fetchAll().getUnchecked()).isEmpty();
+
+    verify(cursor, times(1)).close();
+  }
+
+  @Test
+  public void singleResult() throws Exception {
+    when(cursor.hasNext()).thenReturn(true).thenReturn(false);
+    when(cursor.next()).thenReturn(ImmutableEntity.of("foo"));
+
+    check(repository.findAll().fetchAll().getUnchecked()).has(ImmutableEntity.of("foo"));
+
+    verify(cursor, times(1)).close();
+  }
+
+  @Test
+  public void onException() throws Exception {
+    when(cursor.hasNext()).thenReturn(true);
+    when(cursor.next()).thenThrow(new IllegalStateException("boom"));
+
+    try {
+      repository.findAll().fetchAll().getUnchecked();
+      fail("Shouldn't get here");
+    } catch (Exception ignore) {
+      // expected
+    }
+
+    verify(cursor, times(1)).close();
+  }
+}