Make FileSystemWatcherTests more robust

Previously, several tests in FileSystemWatcherTests assumed that all
of the changes detected by the watcher would be grouped into a single
change set. This assumption breaks down when a test runs slowly (due
to CPU or IO contention, for example), and making changes to the file
system takes long then the watcher's polling interval. When this
happens, the changes will be split across two (or more).

This commit attempts to make the tests more robust. The tests now
tolerate multiple changes sets by combining them and asserting that
across the n change sets, only the expected changes were detected.

Closes gh-25901

Author: wilkinsona

spring-boot-project/spring-boot-devtools/src/test/java/org/springframework/boot/devtools/filewatch/FileSystemWatcherTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -23,10 +23,10 @@
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashSet;
-import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Set;
 import java.util.UUID;
+import java.util.stream.Collectors;
 
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
@@ -44,6 +44,7 @@
  * Tests for {@link FileSystemWatcher}.
  *
  * @author Phillip Webb
+ * @author Andy Wilkinson
  */
 class FileSystemWatcherTests {
 
@@ -120,19 +121,17 @@ void addFile() throws Exception {
 		File directory = startWithNewDirectory();
 		File file = touch(new File(directory, "test.txt"));
 		this.watcher.stopAfter(1);
-		ChangedFiles changedFiles = getSingleChangedFiles();
 		ChangedFile expected = new ChangedFile(directory, file, Type.ADD);
-		assertThat(changedFiles.getFiles()).contains(expected);
+		assertThat(getAllFileChanges()).containsExactly(expected);
 	}
 
 	@Test
 	void addNestedFile() throws Exception {
 		File directory = startWithNewDirectory();
 		File file = touch(new File(new File(directory, "sub"), "text.txt"));
 		this.watcher.stopAfter(1);
-		ChangedFiles changedFiles = getSingleChangedFiles();
 		ChangedFile expected = new ChangedFile(directory, file, Type.ADD);
-		assertThat(changedFiles.getFiles()).contains(expected);
+		assertThat(getAllFileChanges()).containsExactly(expected);
 	}
 
 	@Test
@@ -144,9 +143,8 @@ void createSourceDirectoryAndAddFile() throws IOException {
 		directory.mkdirs();
 		File file = touch(new File(directory, "text.txt"));
 		this.watcher.stopAfter(1);
-		ChangedFiles changedFiles = getSingleChangedFiles();
 		ChangedFile expected = new ChangedFile(directory, file, Type.ADD);
-		assertThat(changedFiles.getFiles()).contains(expected);
+		assertThat(getAllFileChanges()).containsExactly(expected);
 	}
 
 	@Test
@@ -171,8 +169,7 @@ void waitsForQuietPeriod() throws Exception {
 			Thread.sleep(10);
 		}
 		this.watcher.stopAfter(1);
-		ChangedFiles changedFiles = getSingleChangedFiles();
-		assertThat(changedFiles.getFiles()).hasSize(100);
+		assertThat(getAllFileChanges()).hasSize(100);
 	}
 
 	@Test
@@ -184,9 +181,8 @@ void withExistingFiles() throws Exception {
 		this.watcher.start();
 		File file = touch(new File(directory, "test2.txt"));
 		this.watcher.stopAfter(1);
-		ChangedFiles changedFiles = getSingleChangedFiles();
 		ChangedFile expected = new ChangedFile(directory, file, Type.ADD);
-		assertThat(changedFiles.getFiles()).contains(expected);
+		assertThat(getAllFileChanges()).contains(expected);
 	}
 
 	@Test
@@ -201,7 +197,7 @@ void multipleSources() throws Exception {
 		File file1 = touch(new File(directory1, "test.txt"));
 		File file2 = touch(new File(directory2, "test.txt"));
 		this.watcher.stopAfter(1);
-		Set<ChangedFiles> change = getSingleOnChange();
+		Set<ChangedFiles> change = this.changes.stream().flatMap(Set<ChangedFiles>::stream).collect(Collectors.toSet());
 		assertThat(change.size()).isEqualTo(2);
 		for (ChangedFiles changedFiles : change) {
 			if (changedFiles.getSourceDirectory().equals(directory1)) {
@@ -219,16 +215,16 @@ void multipleSources() throws Exception {
 	void multipleListeners() throws Exception {
 		File directory = new File(this.tempDir, UUID.randomUUID().toString());
 		directory.mkdir();
-		final Set<ChangedFiles> listener2Changes = new LinkedHashSet<>();
+		final List<Set<ChangedFiles>> listener2Changes = new ArrayList<>();
 		this.watcher.addSourceDirectory(directory);
-		this.watcher.addListener(listener2Changes::addAll);
+		this.watcher.addListener(listener2Changes::add);
 		this.watcher.start();
 		File file = touch(new File(directory, "test.txt"));
 		this.watcher.stopAfter(1);
-		ChangedFiles changedFiles = getSingleChangedFiles();
 		ChangedFile expected = new ChangedFile(directory, file, Type.ADD);
-		assertThat(changedFiles.getFiles()).contains(expected);
-		assertThat(listener2Changes).isEqualTo(this.changes.get(0));
+		Set<ChangedFile> changeSet = getAllFileChanges();
+		assertThat(changeSet).contains(expected);
+		assertThat(getAllFileChanges(listener2Changes)).isEqualTo(changeSet);
 	}
 
 	@Test
@@ -243,8 +239,7 @@ void modifyDeleteAndAdd() throws Exception {
 		delete.delete();
 		File add = touch(new File(directory, "add.txt"));
 		this.watcher.stopAfter(1);
-		ChangedFiles changedFiles = getSingleChangedFiles();
-		Set<ChangedFile> actual = changedFiles.getFiles();
+		Set<ChangedFile> actual = getAllFileChanges();
 		Set<ChangedFile> expected = new HashSet<>();
 		expected.add(new ChangedFile(directory, modify, Type.MODIFY));
 		expected.add(new ChangedFile(directory, delete, Type.DELETE));
@@ -266,8 +261,7 @@ void withTriggerFilter() throws Exception {
 		assertThat(this.changes).isEmpty();
 		FileCopyUtils.copy("abc".getBytes(), trigger);
 		this.watcher.stopAfter(1);
-		ChangedFiles changedFiles = getSingleChangedFiles();
-		Set<ChangedFile> actual = changedFiles.getFiles();
+		Set<ChangedFile> actual = getAllFileChanges();
 		Set<ChangedFile> expected = new HashSet<>();
 		expected.add(new ChangedFile(directory, file, Type.MODIFY));
 		assertThat(actual).isEqualTo(expected);
@@ -286,15 +280,13 @@ private File startWithNewDirectory() throws IOException {
 		return directory;
 	}
 
-	private ChangedFiles getSingleChangedFiles() {
-		Set<ChangedFiles> singleChange = getSingleOnChange();
-		assertThat(singleChange).hasSize(1);
-		return singleChange.iterator().next();
+	private Set<ChangedFile> getAllFileChanges() {
+		return getAllFileChanges(this.changes);
 	}
 
-	private Set<ChangedFiles> getSingleOnChange() {
-		assertThat(this.changes).hasSize(1);
-		return this.changes.get(0);
+	private Set<ChangedFile> getAllFileChanges(List<Set<ChangedFiles>> changes) {
+		return changes.stream().flatMap(Set<ChangedFiles>::stream)
+				.flatMap((changedFiles) -> changedFiles.getFiles().stream()).collect(Collectors.toSet());
 	}
 
 	private File touch(File file) throws IOException {