Add utility test class for single item reading scenarios

Author: fmbenhassine

spring-batch-core/src/test/java/org/springframework/batch/core/step/item/SingleItemStreamReader.java

@@ -0,0 +1,66 @@
+/*
+ * Copyright 2025-present 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
+ *
+ *      https://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.batch.core.step.item;
+
+import org.jspecify.annotations.Nullable;
+
+import org.springframework.batch.infrastructure.item.ExecutionContext;
+import org.springframework.batch.infrastructure.item.ItemStreamException;
+import org.springframework.batch.infrastructure.item.ItemStreamReader;
+
+/**
+ * An {@link ItemStreamReader} that reads a single item. Useful for testing purposes.
+ *
+ * @param <T> the type of item to be read
+ * @author Mahmoud Ben Hassine
+ */
+public class SingleItemStreamReader<T> implements ItemStreamReader<T> {
+
+	private T item;
+
+	private final T initialValue;
+
+	/**
+	 * Create a new {@link SingleItemStreamReader} with the given initial value.
+	 * @param initialValue the initial value to be read
+	 */
+	public SingleItemStreamReader(T initialValue) {
+		this.initialValue = initialValue;
+	}
+
+	@Override
+	public @Nullable T read() throws Exception {
+		T returnedItem = this.item;
+		this.item = null;
+		return returnedItem;
+	}
+
+	@Override
+	public void open(ExecutionContext executionContext) throws ItemStreamException {
+		this.item = this.initialValue;
+	}
+
+	@Override
+	public void update(ExecutionContext executionContext) throws ItemStreamException {
+		this.item = null;
+	}
+
+	@Override
+	public void close() throws ItemStreamException {
+		this.item = null;
+	}
+
+}