Fix race condition with in file-split-ftp

https://build.spring.io/browse/INTSAMPLES-NIGHTLY-2398/

* Remove `FileExistsMode.APPEND_NO_FLUSH` from the app.
It's not reliable for unit testing: keeps resources opened and cause
false positive assertions but at the same time no any interactions with
mock `session`
* Clean up test directories before and after tests

applications/file-split-ftp/src/main/java/org/springframework/integration/samples/filesplit/Application.java

@@ -37,7 +37,6 @@ import org.springframework.integration.file.dsl.FileWritingMessageHandlerSpec;
 import org.springframework.integration.file.dsl.Files;
 import org.springframework.integration.file.remote.session.SessionFactory;
 import org.springframework.integration.file.splitter.FileSplitter;
-import org.springframework.integration.file.support.FileExistsMode;
 import org.springframework.integration.ftp.dsl.Ftp;
 import org.springframework.integration.ftp.session.DefaultFtpSessionFactory;
 import org.springframework.integration.http.config.EnableIntegrationGraphController;
@@ -94,8 +93,7 @@ public class Application {
 	public FileWritingMessageHandlerSpec fileOut() {
 		return Files.outboundAdapter("'/tmp/out'")
 				.appendNewLine(true)
-				.fileNameExpression("payload.substring(1, 4) + '.txt'")
-				.fileExistsMode(FileExistsMode.APPEND_NO_FLUSH); // files remain open for efficiency
+				.fileNameExpression("payload.substring(1, 4) + '.txt'");
 	}
 
 	/**

applications/file-split-ftp/src/test/java/org/springframework/integration/samples/filesplit/ApplicationTests.java

@@ -22,7 +22,6 @@ import static org.mockito.ArgumentMatchers.eq;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.BDDMockito.willThrow;
 import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.reset;
 import static org.mockito.Mockito.verify;
 
 import java.io.BufferedReader;
@@ -33,7 +32,9 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.util.List;
 
+import org.apache.commons.io.FileUtils;
 import org.apache.commons.net.ftp.FTPFile;
+import org.junit.After;
 import org.junit.Before;
 import org.junit.BeforeClass;
 import org.junit.Test;
@@ -72,21 +73,27 @@ public class ApplicationTests {
 	public static void setup() {
 		// Configure the boot property to send email to the test email server.
 		System.setProperty("spring.mail.port", Integer.toString(smtpServer.getPort()));
-		new File("/tmp/in/foo.txt").delete();
-		new File("/tmp/in/foo.txt.success").delete();
-		new File("/tmp/in/foo.txt.failed").delete();
 	}
 
 	@Before
-	public void beforeTest() {
+	public void beforeTest() throws IOException {
 		smtpServer.getMessages().clear();
+
+		FileUtils.cleanDirectory(new File("/tmp/in"));
+		FileUtils.cleanDirectory(new File("/tmp/out"));
+
 		this.fileInboundChannelAdapter.start();
 	}
 
+	@After
+	public void tearDown() throws IOException {
+		FileUtils.cleanDirectory(new File("/tmp/in"));
+		FileUtils.cleanDirectory(new File("/tmp/out"));
+	}
+
 	@SuppressWarnings("unchecked")
 	@Test
 	public void testSuccess() throws Exception {
-		reset(this.session);
 		String message = runTest(false);
 		assertThat(message).contains("File successfully split and transferred");
 		assertThat(message).contains(TestUtils.applySystemFileSeparator("/tmp/in/foo.txt"));
@@ -95,7 +102,7 @@ public class ApplicationTests {
 	@Test
 	public void testFailure() throws Exception {
 		willThrow(new RuntimeException("fail test exception"))
-			.given(this.session).write(any(InputStream.class), eq("foo/002.txt.writing"));
+				.given(this.session).write(any(InputStream.class), eq("foo/002.txt.writing"));
 		String message = runTest(true);
 		assertThat(message).contains("File split and transfer failed");
 		assertThat(message).contains("fail test exception");
@@ -116,34 +123,31 @@ public class ApplicationTests {
 		in.renameTo(new File("/tmp/in/", "foo.txt"));
 		File out = new File("/tmp/out/002.txt");
 		int n = 0;
-		while(n++ < 100 && (!out.exists() || out.length() < 12)) {
+		while (n++ < 100 && (!out.exists() || out.length() < 12)) {
 			Thread.sleep(100);
 		}
 		assertThat(out.exists()).isTrue();
 		BufferedReader br = new BufferedReader(new FileReader(out));
 		assertThat(br.readLine()).isEqualTo("*002,foo,bar");
 		br.close();
-		out.delete();
 		out = new File("/tmp/out/006.txt");
 		n = 0;
-		while(n++ < 100 && (!out.exists() || out.length() < 12)) {
+		while (n++ < 100 && (!out.exists() || out.length() < 12)) {
 			Thread.sleep(100);
 		}
 		assertThat(out.exists()).isTrue();
 		br = new BufferedReader(new FileReader(out));
 		assertThat(br.readLine()).isEqualTo("*006,baz,qux");
 		br.close();
-		out.delete();
 		out = new File("/tmp/out/009.txt");
 		n = 0;
-		while(n++ < 100 && (!out.exists() || out.length() < 12)) {
+		while (n++ < 100 && (!out.exists() || out.length() < 12)) {
 			Thread.sleep(100);
 		}
 		assertThat(out.exists()).isTrue();
 		br = new BufferedReader(new FileReader(out));
 		assertThat(br.readLine()).isEqualTo("*009,fiz,buz");
 		br.close();
-		out.delete();
 		if (!fail) {
 			in = new File("/tmp/in/", "foo.txt.success");
 		}
@@ -151,11 +155,10 @@ public class ApplicationTests {
 			in = new File("/tmp/in/", "foo.txt.failed");
 		}
 		n = 0;
-		while(n++ < 100 && !in.exists()) {
+		while (n++ < 100 && !in.exists()) {
 			Thread.sleep(100);
 		}
 		assertThat(in.exists()).isTrue();
-		in.delete();
 		// verify FTP
 		verify(this.session).write(any(InputStream.class), eq("foo/002.txt.writing"));
 		if (!fail) {