#146 - Added tests and simplified condition.

Added tests to verify behaviour.
In order to improve testability querying was extracted into package private method.

The condition avoiding the IN-queries with empty parameter lists was simplified and made less lenient.

Original pull request: #147.

src/main/java/org/springframework/data/envers/repository/support/EnversRevisionRepositoryImpl.java

@@ -90,7 +90,7 @@ public class EnversRevisionRepositoryImpl<T, ID, N extends Number & Comparable<N
 		Class<T> type = entityInformation.getJavaType();
 		AuditReader reader = AuditReaderFactory.get(entityManager);
 
-		List<Number> revisions = reader.getRevisions(type, id);
+		List<Number> revisions = getRevisions(id, type, reader);
 
 		if (revisions.isEmpty()) {
 			return Optional.empty();
@@ -129,7 +129,7 @@ public class EnversRevisionRepositoryImpl<T, ID, N extends Number & Comparable<N
 
 		Class<T> type = entityInformation.getJavaType();
 		AuditReader reader = AuditReaderFactory.get(entityManager);
-		List<? extends Number> revisionNumbers = reader.getRevisions(type, id);
+		List<? extends Number> revisionNumbers = getRevisions(id, type, reader);
 
 		return revisionNumbers.isEmpty() ? Revisions.none()
 				: getEntitiesForRevisions((List<N>) revisionNumbers, id, reader);
@@ -144,14 +144,15 @@ public class EnversRevisionRepositoryImpl<T, ID, N extends Number & Comparable<N
 
 		Class<T> type = entityInformation.getJavaType();
 		AuditReader reader = AuditReaderFactory.get(entityManager);
-		List<Number> revisionNumbers = reader.getRevisions(type, id);
+		List<Number> revisionNumbers = getRevisions((ID) id, (Class<T>) type, reader);
 		boolean isDescending = RevisionSort.getRevisionDirection(pageable.getSort()).isDescending();
 
 		if (isDescending) {
 			Collections.reverse(revisionNumbers);
 		}
 
-		if (revisionNumbers.isEmpty() || pageable.getOffset() > revisionNumbers.size()) {
+		if (
+				pageable.getOffset() >= revisionNumbers.size()) {
 			return Page.empty(pageable);
 		}
 
@@ -166,6 +167,10 @@ public class EnversRevisionRepositoryImpl<T, ID, N extends Number & Comparable<N
 		return new PageImpl<Revision<N, T>>(revisions.getContent(), pageable, revisionNumbers.size());
 	}
 
+	List<Number> getRevisions(ID id, Class<T> type, AuditReader reader) {
+		return reader.getRevisions(type, id);
+	}
+
 	/**
 	 * Returns the entities in the given revisions for the entitiy with the given id.
 	 *

src/test/java/org/springframework/data/envers/repository/support/EnversRevisionRepositoryImplUnitTests.java

@@ -0,0 +1,101 @@
+/*
+ * Copyright 2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.data.envers.repository.support;
+
+import static org.mockito.Mockito.*;
+
+import javax.persistence.EntityManager;
+
+import org.hibernate.HibernateException;
+import org.hibernate.Session;
+import org.hibernate.engine.spi.SessionImplementor;
+import org.hibernate.envers.AuditReader;
+import org.hibernate.envers.boot.internal.EnversService;
+import org.junit.Before;
+import org.junit.Test;
+import org.springframework.data.domain.PageRequest;
+import org.springframework.data.jpa.repository.support.JpaEntityInformation;
+import org.springframework.data.repository.history.support.RevisionEntityInformation;
+
+import java.util.Collections;
+import java.util.List;
+
+/**
+ * Unit tests for EversRevisionRepositoryImpl.
+ *
+ * @author Jens Schauder
+ */
+public class EnversRevisionRepositoryImplUnitTests {
+
+	private static final int NON_EXISTING_ID = -999;
+
+	JpaEntityInformation<?, ?> entityInformation = mock(JpaEntityInformation.class);
+	RevisionEntityInformation revisionEntityInformation = mock(RevisionEntityInformation.class);
+	SessionImplementor session = mock(SessionImplementor.class, RETURNS_DEEP_STUBS);
+	EnversService enversService = mock(EnversService.class, RETURNS_DEEP_STUBS);
+	EntityManager entityManager = mock(EntityManager.class);
+
+
+	@Before
+	public void mockHibernateInfrastructure() {
+
+		when(entityInformation.getJavaType()).thenReturn((Class) DummyEntity.class);
+
+		when(enversService.getEntitiesConfigurations().isVersioned(any(String.class))).thenReturn(true);
+
+		when(session.isOpen()).thenReturn(true);
+		when(session.getFactory().getServiceRegistry().getService(EnversService.class)).thenReturn(enversService);
+
+		when(entityManager.getDelegate()).thenReturn(session);
+	}
+
+	@Test // #146
+	public void findRevisionShortCircuitsOnEmptyRevisionList() {
+
+		failOnEmptyRevisions();
+
+		EnversRevisionRepositoryImplUnderTest<?, Object, ?> repository = new EnversRevisionRepositoryImplUnderTest<>(entityInformation, revisionEntityInformation, entityManager);
+
+		repository.findRevisions(-999, PageRequest.of(0, 5));
+	}
+
+	private void failOnEmptyRevisions() {
+
+		// simulate failure to query with empty revisions list as Postgres does.
+		when(enversService.getRevisionInfoQueryCreator().getRevisionsQuery(any(Session.class), eq(Collections.emptySet()))
+				.getResultList()).thenThrow(HibernateException.class);
+	}
+
+	/**
+	 * An extension for the {@link EnversRevisionRepositoryImpl} that skips accessing the AuditReader and always returns an empty List.
+	 */
+	private class EnversRevisionRepositoryImplUnderTest<T, ID, N extends Number & Comparable<N>>
+			extends EnversRevisionRepositoryImpl<T, ID, N> {
+
+		EnversRevisionRepositoryImplUnderTest(JpaEntityInformation<T, ?> entityInformation,
+				RevisionEntityInformation revisionEntityInformation, EntityManager entityManager) {
+			super(entityInformation, revisionEntityInformation, entityManager);
+		}
+
+		@Override
+		List<Number> getRevisions(ID id, Class<T> type, AuditReader reader) {
+			return Collections.emptyList();
+		}
+	}
+
+	private static class DummyEntity {
+	}
+}

src/test/java/org/springframework/data/envers/repository/support/RepositoryIntegrationTests.java

@@ -183,4 +183,25 @@ public class RepositoryIntegrationTests {
 				.extracting(c -> c.name, c -> c.code) //
 				.containsExactly(null, null);
 	}
+
+	@Test // #146
+	public void shortCurcuitingWhenOffsetIsToLarge() {
+		Country de = new Country();
+		de.code = "de";
+		de.name = "Deutschland";
+
+		countryRepository.save(de);
+
+		countryRepository.delete(de);
+
+		check(de, 0, 1);
+		check(de, 1, 1);
+		check(de, 2, 0);
+	}
+
+	void check(Country de, int page, int expectedSize) {
+
+		Page<Revision<Integer, Country>> revisions = countryRepository.findRevisions(de.id, PageRequest.of(page,1));
+		assertThat(revisions).hasSize(expectedSize);
+	}
 }