Add unit tests for o.s.b.d.g.function.support.SingleResultReturningCollector.

geode-spring-boot-starter/src/main/java/org/springframework/boot/data/geode/function/support/SingleResultReturningCollector.java

@@ -44,20 +44,24 @@ public class SingleResultReturningCollector<T> extends AbstractResultCollector<T
 	private <T> T extractSingleResult(Object result) {
 
 		return (T) Optional.ofNullable(result)
-			.filter(this::isInstanceOfIterable)
-			.map(it -> (Iterable<T>) it)
+			.filter(this::isInstanceOfIterableOrIterator)
 			.map(this::toIterator)
 			.filter(Iterator::hasNext)
 			.map(Iterator::next)
 			.map(this::extractSingleResult)
-			.orElse(result);
+			.orElseGet(() -> isInstanceOfIterableOrIterator(result) ? null : result);
 	}
 
-	private boolean isInstanceOfIterable(Object obj) {
-		return obj instanceof Iterable;
+	private boolean isInstanceOfIterableOrIterator(Object obj) {
+		return obj instanceof Iterable || obj instanceof Iterator;
 	}
 
-	private <T> Iterator<T> toIterator(Iterable<T> obj) {
-		return obj != null ? obj.iterator() : Collections.emptyIterator();
+	@SuppressWarnings("unchecked")
+	private <T> Iterator<T> toIterator(Object obj) {
+		return obj instanceof Iterator ? (Iterator<T>) obj : toIterator((Iterable<T>) obj);
+	}
+
+	private <T> Iterator<T> toIterator(Iterable<T> iterable) {
+		return iterable != null ? iterable.iterator() : Collections.emptyIterator();
 	}
 }

geode-spring-boot-starter/src/test/java/org/springframework/boot/data/geode/function/support/SingleResultReturningCollectorUnitTests.java

@@ -0,0 +1,130 @@
+/*
+ * 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.boot.data.geode.function.support;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+import java.util.Arrays;
+
+import org.apache.geode.distributed.DistributedMember;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.mockito.Mock;
+import org.mockito.junit.MockitoJUnitRunner;
+
+/**
+ * Unit tests for {@link SingleResultReturningCollector}.
+ *
+ * @author John Blum
+ * @see org.junit.Test
+ * @see org.mockito.Mock
+ * @see org.mockito.Mockito
+ * @see org.mockito.junit.MockitoJUnitRunner
+ * @see org.springframework.boot.data.geode.function.support.SingleResultReturningCollector
+ * @since 1.0.0
+ */
+@RunWith(MockitoJUnitRunner.class)
+public class SingleResultReturningCollectorUnitTests {
+
+	@Mock
+	private DistributedMember mockDistributedMember;
+
+	private SingleResultReturningCollector<Object> resultCollector;
+
+	@Before
+	public void setup() {
+		this.resultCollector = new SingleResultReturningCollector<>();
+	}
+
+	@Test
+	public void addResultWithNullIsSafe() {
+
+		assertThat(this.resultCollector.getResult()).isNull();
+
+		this.resultCollector.addResult(this.mockDistributedMember, null);
+
+		assertThat(this.resultCollector.getResult()).isNull();
+	}
+
+	@Test
+	public void addResultWithSingleObjectReturnsObject() {
+
+		assertThat(this.resultCollector.getResult()).isNull();
+
+		this.resultCollector.addResult(this.mockDistributedMember, "test");
+
+		assertThat(this.resultCollector.getResult()).isEqualTo("test");
+	}
+
+	@Test
+	public void addResultWithIterableReturnsFirstElement() {
+
+		Iterable<String> list = Arrays.asList("one", "two", "three");
+
+		assertThat(this.resultCollector.getResult()).isNull();
+
+		this.resultCollector.addResult(this.mockDistributedMember, list);
+
+		assertThat(this.resultCollector.getResult()).isEqualTo("one");
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	public void addResultWithIterableReturningNullIteratorIsSafe() {
+
+		Iterable<Object> mockIterable = mock(Iterable.class);
+
+		when(mockIterable.iterator()).thenReturn(null);
+
+		assertThat(this.resultCollector.getResult()).isNull();
+
+		this.resultCollector.addResult(mockDistributedMember, mockIterable);
+
+		assertThat(this.resultCollector.getResult()).isNull();
+	}
+
+	@Test
+	public void addResultWithIterableOfListsReturnsFirstElementInListOne() {
+
+		Iterable<String> listOne = Arrays.asList("one", "two", "three");
+		Iterable<String> listTwo = Arrays.asList("four", "five", "six");
+
+		assertThat(this.resultCollector.getResult()).isNull();
+
+		this.resultCollector.addResult(this.mockDistributedMember, Arrays.asList(listOne, listTwo));
+
+		assertThat(this.resultCollector.getResult()).isEqualTo("one");
+	}
+
+	@Test
+	public void addResultWithIterableOfListsOfListsReturnsFirstElementInListOne() {
+
+		Iterable<String> listOne = Arrays.asList("one", "two", "three");
+		Iterable<String> listTwo = Arrays.asList("four", "five", "six");
+		Iterable<String> listThree = Arrays.asList("seven", "eight", "nine");
+
+		assertThat(this.resultCollector.getResult()).isNull();
+
+		this.resultCollector.addResult(this.mockDistributedMember,
+			Arrays.asList(Arrays.asList(listOne, listTwo), listThree));
+
+		assertThat(this.resultCollector.getResult()).isEqualTo("one");
+	}
+}