Add FileDocumentWriterTest for FileDocumentWriter default constructor and various options

Auto-cherry-pick to 1.0.x
Fixes #3646

Signed-off-by: Jemin Huh <[email protected]>

Author: JM-Lab

spring-ai-commons/src/test/java/org/springframework/ai/writer/FileDocumentWriterTest.java

@@ -0,0 +1,145 @@
+package org.springframework.ai.writer;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+import org.springframework.ai.document.Document;
+import org.springframework.ai.document.MetadataMode;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * @author Jemin Huh
+ */
+public class FileDocumentWriterTest {
+
+	@TempDir
+	Path tempDir;
+
+	private String testFileName;
+
+	private List<Document> testDocuments;
+
+	@BeforeEach
+	void setUp() {
+		testFileName = tempDir.resolve("file-document-test-output.txt").toString();
+		testDocuments = List.of(
+				Document.builder()
+					.text("Document one introduces the core functionality of Spring AI.")
+					.metadata("page_number", "1")
+					.metadata("end_page_number", "2")
+					.metadata("source", "intro.pdf")
+					.metadata("title", "Spring AI Overview")
+					.metadata("author", "QA Team")
+					.build(),
+				Document.builder()
+					.text("Document two illustrates multi-line handling and line breaks.\nEnsure preservation of formatting.")
+					.metadata("page_number", "3")
+					.metadata("end_page_number", "4")
+					.metadata("source", "formatting.pdf")
+					.build(),
+				Document.builder()
+					.text("Document three checks metadata inclusion and output formatting behavior.")
+					.metadata("page_number", "5")
+					.metadata("end_page_number", "6")
+					.metadata("version", "v1.2")
+					.build());
+	}
+
+	@Test
+	void testBasicWrite() throws IOException {
+		var writer = new FileDocumentWriter(testFileName);
+		writer.accept(testDocuments);
+
+		List<String> lines = Files.readAllLines(Path.of(testFileName));
+		assertEquals("", lines.get(0));
+		assertEquals("", lines.get(1));
+		assertEquals("Document one introduces the core functionality of Spring AI.", lines.get(2));
+		assertEquals("", lines.get(3));
+		assertEquals("Document two illustrates multi-line handling and line breaks.", lines.get(4));
+		assertEquals("Ensure preservation of formatting.", lines.get(5));
+		assertEquals("", lines.get(6));
+		assertEquals("Document three checks metadata inclusion and output formatting behavior.", lines.get(7));
+	}
+
+	@Test
+	void testWriteWithDocumentMarkers() throws IOException {
+		var writer = new FileDocumentWriter(testFileName, true, MetadataMode.NONE, false);
+		writer.accept(testDocuments);
+
+		List<String> lines = Files.readAllLines(Path.of(testFileName));
+		assertEquals("", lines.get(0));
+		assertEquals("### Doc: 0, pages:[1,2]", lines.get(1));
+		assertEquals("", lines.get(2));
+		assertEquals("", lines.get(3));
+		assertEquals("Document one introduces the core functionality of Spring AI.", lines.get(4));
+		assertEquals("### Doc: 1, pages:[3,4]", lines.get(5));
+		assertEquals("", lines.get(6));
+		assertEquals("", lines.get(7));
+		assertEquals("Document two illustrates multi-line handling and line breaks.", lines.get(8));
+		assertEquals("Ensure preservation of formatting.", lines.get(9));
+		assertEquals("### Doc: 2, pages:[5,6]", lines.get(10));
+		assertEquals("", lines.get(11));
+		assertEquals("", lines.get(12));
+		assertEquals("Document three checks metadata inclusion and output formatting behavior.", lines.get(13));
+	}
+
+	@Test
+	void testMetadataModeAllWithDocumentMarkers() throws IOException {
+		var writer = new FileDocumentWriter(testFileName, true, MetadataMode.ALL, false);
+		writer.accept(testDocuments);
+
+		List<String> lines = Files.readAllLines(Path.of(testFileName));
+		assertEquals("", lines.get(0));
+		assertEquals("### Doc: 0, pages:[1,2]", lines.get(1));
+		String subListToString = lines.subList(2, 7).toString();
+		assertTrue(subListToString.contains("page_number: 1"));
+		assertTrue(subListToString.contains("end_page_number: 2"));
+		assertTrue(subListToString.contains("source: intro.pdf"));
+		assertTrue(subListToString.contains("title: Spring AI Overview"));
+		assertTrue(subListToString.contains("author: QA Team"));
+		assertEquals("", lines.get(7));
+		assertEquals("Document one introduces the core functionality of Spring AI.", lines.get(8));
+
+		assertEquals("### Doc: 1, pages:[3,4]", lines.get(9));
+		subListToString = lines.subList(10, 13).toString();
+		assertTrue(subListToString.contains("page_number: 3"));
+		assertTrue(subListToString.contains("source: formatting.pdf"));
+		assertTrue(subListToString.contains("end_page_number: 4"));
+		assertEquals("", lines.get(13));
+		assertEquals("Document two illustrates multi-line handling and line breaks.", lines.get(14));
+		assertEquals("Ensure preservation of formatting.", lines.get(15));
+
+		assertEquals("### Doc: 2, pages:[5,6]", lines.get(16));
+		subListToString = lines.subList(17, 20).toString();
+		assertTrue(subListToString.contains("page_number: 5"));
+		assertTrue(subListToString.contains("end_page_number: 6"));
+		assertTrue(subListToString.contains("version: v1.2"));
+		assertEquals("", lines.get(20));
+		assertEquals("Document three checks metadata inclusion and output formatting behavior.", lines.get(21));
+	}
+
+	@Test
+	void testAppendWrite() throws IOException {
+		Files.writeString(Path.of(testFileName), "Test String\n");
+
+		var writer = new FileDocumentWriter(testFileName, false, MetadataMode.NONE, true);
+		writer.accept(testDocuments.subList(0, 2));
+
+		List<String> lines = Files.readAllLines(Path.of(testFileName));
+		assertEquals("Test String", lines.get(0));
+		assertEquals("", lines.get(1));
+		assertEquals("", lines.get(2));
+		assertEquals("Document one introduces the core functionality of Spring AI.", lines.get(3));
+		assertEquals("", lines.get(4));
+		assertEquals("Document two illustrates multi-line handling and line breaks.", lines.get(5));
+		assertEquals("Ensure preservation of formatting.", lines.get(6));
+		assertEquals(7, lines.size());
+	}
+
+}