Java example source code file (FilesTest.java)

This example Java source code file (FilesTest.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

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Java - Java tags/keywords

bytearrayoutputstream, byteprocessor, closer, file, fileinputstream, illegalargumentexception, ioexception, lineprocessor, list, nio, nullpointerexception, override, string, throwable, unmovablefile, util

The FilesTest.java Java example source code

/*
 * Copyright (C) 2007 The Guava 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 com.google.common.io;

import static com.google.common.io.Files.createTempDir;
import static com.google.common.io.Files.touch;
import static com.google.common.truth.Truth.assertThat;

import com.google.common.base.Charsets;
import com.google.common.collect.ImmutableList;
import com.google.common.hash.Hashing;
import com.google.common.primitives.Bytes;

import junit.framework.TestSuite;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.io.RandomAccessFile;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel.MapMode;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Random;

/**
 * Unit test for {@link Files}.
 *
 * @author Chris Nokleberg
 */

public class FilesTest extends IoTestCase {

  public static TestSuite suite() {
    TestSuite suite = new TestSuite();
    suite.addTest(ByteSourceTester.tests("Files.asByteSource[File]",
        SourceSinkFactories.fileByteSourceFactory(), true));
    suite.addTest(ByteSinkTester.tests("Files.asByteSink[File]",
        SourceSinkFactories.fileByteSinkFactory()));
    suite.addTest(ByteSinkTester.tests("Files.asByteSink[File, APPEND]",
        SourceSinkFactories.appendingFileByteSinkFactory()));
    suite.addTest(CharSourceTester.tests("Files.asCharSource[File, Charset]",
        SourceSinkFactories.fileCharSourceFactory(), false));
    suite.addTest(CharSinkTester.tests("Files.asCharSink[File, Charset]",
        SourceSinkFactories.fileCharSinkFactory()));
    suite.addTest(CharSinkTester.tests("Files.asCharSink[File, Charset, APPEND]",
        SourceSinkFactories.appendingFileCharSinkFactory()));
    suite.addTestSuite(FilesTest.class);
    return suite;
  }

  public void testRoundTripSources() throws Exception {
    File asciiFile = getTestFile("ascii.txt");
    ByteSource byteSource = Files.asByteSource(asciiFile);
    assertSame(byteSource,
        byteSource.asCharSource(Charsets.UTF_8).asByteSource(Charsets.UTF_8));
  }

  public void testToByteArray() throws IOException {
    File asciiFile = getTestFile("ascii.txt");
    File i18nFile = getTestFile("i18n.txt");
    assertTrue(Arrays.equals(ASCII.getBytes(Charsets.US_ASCII),
        Files.toByteArray(asciiFile)));
    assertTrue(Arrays.equals(I18N.getBytes(Charsets.UTF_8),
        Files.toByteArray(i18nFile)));
    assertTrue(Arrays.equals(I18N.getBytes(Charsets.UTF_8),
        Files.asByteSource(i18nFile).read()));
  }

  public void testReadFile_withCorrectSize() throws IOException {
    File asciiFile = getTestFile("ascii.txt");

    Closer closer = Closer.create();
    try {
      InputStream in = closer.register(new FileInputStream(asciiFile));
      byte[] bytes = Files.readFile(in, asciiFile.length());
      assertTrue(Arrays.equals(ASCII.getBytes(Charsets.US_ASCII), bytes));
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  public void testReadFile_withSmallerSize() throws IOException {
    File asciiFile = getTestFile("ascii.txt");

    Closer closer = Closer.create();
    try {
      InputStream in = closer.register(new FileInputStream(asciiFile));
      byte[] bytes = Files.readFile(in, 10);
      assertTrue(Arrays.equals(ASCII.getBytes(Charsets.US_ASCII), bytes));
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  public void testReadFile_withLargerSize() throws IOException {
    File asciiFile = getTestFile("ascii.txt");

    Closer closer = Closer.create();
    try {
      InputStream in = closer.register(new FileInputStream(asciiFile));
      byte[] bytes = Files.readFile(in, 500);
      assertTrue(Arrays.equals(ASCII.getBytes(Charsets.US_ASCII), bytes));
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  public void testReadFile_withSizeZero() throws IOException {
    File asciiFile = getTestFile("ascii.txt");

    Closer closer = Closer.create();
    try {
      InputStream in = closer.register(new FileInputStream(asciiFile));
      byte[] bytes = Files.readFile(in, 0);
      assertTrue(Arrays.equals(ASCII.getBytes(Charsets.US_ASCII), bytes));
    } catch (Throwable e) {
      throw closer.rethrow(e);
    } finally {
      closer.close();
    }
  }

  /**
   * A {@link File} that provides a specialized value for {@link File#length()}.
   */
  private static class BadLengthFile extends File {

    private final long badLength;

    public BadLengthFile(File delegate, long badLength) {
      super(delegate.getPath());
      this.badLength = badLength;
    }

    @Override
    public long length() {
      return badLength;
    }

    private static final long serialVersionUID = 0;
  }

  public void testToString() throws IOException {
    File asciiFile = getTestFile("ascii.txt");
    File i18nFile = getTestFile("i18n.txt");
    assertEquals(ASCII, Files.toString(asciiFile, Charsets.US_ASCII));
    assertEquals(I18N, Files.toString(i18nFile, Charsets.UTF_8));
    assertThat(Files.toString(i18nFile, Charsets.US_ASCII))
        .isNotEqualTo(I18N);
  }

  public void testWriteString() throws IOException {
    File temp = createTempFile();
    Files.write(I18N, temp, Charsets.UTF_16LE);
    assertEquals(I18N, Files.toString(temp, Charsets.UTF_16LE));
  }

  public void testWriteBytes() throws IOException {
    File temp = createTempFile();
    byte[] data = newPreFilledByteArray(2000);
    Files.write(data, temp);
    assertTrue(Arrays.equals(data, Files.toByteArray(temp)));

    try {
      Files.write(null, temp);
      fail("expected exception");
    } catch (NullPointerException expected) {
    }
  }

  public void testAppendString() throws IOException {
    File temp = createTempFile();
    Files.append(I18N, temp, Charsets.UTF_16LE);
    assertEquals(I18N, Files.toString(temp, Charsets.UTF_16LE));
    Files.append(I18N, temp, Charsets.UTF_16LE);
    assertEquals(I18N + I18N, Files.toString(temp, Charsets.UTF_16LE));
    Files.append(I18N, temp, Charsets.UTF_16LE);
    assertEquals(I18N + I18N + I18N, Files.toString(temp, Charsets.UTF_16LE));
  }

  public void testCopyToOutputStream() throws IOException {
    File i18nFile = getTestFile("i18n.txt");
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    Files.copy(i18nFile, out);
    assertEquals(I18N, out.toString("UTF-8"));
  }

  public void testCopyToAppendable() throws IOException {
    File i18nFile = getTestFile("i18n.txt");
    StringBuilder sb = new StringBuilder();
    Files.copy(i18nFile, Charsets.UTF_8, sb);
    assertEquals(I18N, sb.toString());
  }

  public void testCopyFile() throws IOException {
    File i18nFile = getTestFile("i18n.txt");
    File temp = createTempFile();
    Files.copy(i18nFile, temp);
    assertEquals(I18N, Files.toString(temp, Charsets.UTF_8));
  }

  public void testCopyEqualFiles() throws IOException {
    File temp1 = createTempFile();
    File temp2 = file(temp1.getPath());
    assertEquals(temp1, temp2);
    Files.write(ASCII, temp1, Charsets.UTF_8);
    try {
      Files.copy(temp1, temp2);
      fail("Expected an IAE to be thrown but wasn't");
    } catch (IllegalArgumentException expected) {
    }
    assertEquals(ASCII, Files.toString(temp1, Charsets.UTF_8));
  }

  public void testCopySameFile() throws IOException {
    File temp = createTempFile();
    Files.write(ASCII, temp, Charsets.UTF_8);
    try {
      Files.copy(temp, temp);
      fail("Expected an IAE to be thrown but wasn't");
    } catch (IllegalArgumentException expected) {
    }
    assertEquals(ASCII, Files.toString(temp, Charsets.UTF_8));
  }

  public void testCopyIdenticalFiles() throws IOException {
    File temp1 = createTempFile();
    Files.write(ASCII, temp1, Charsets.UTF_8);
    File temp2 = createTempFile();
    Files.write(ASCII, temp2, Charsets.UTF_8);
    Files.copy(temp1, temp2);
    assertEquals(ASCII, Files.toString(temp1, Charsets.UTF_8));
  }

  public void testEqual() throws IOException {
    File asciiFile = getTestFile("ascii.txt");
    File i18nFile = getTestFile("i18n.txt");
    assertFalse(Files.equal(asciiFile, i18nFile));
    assertTrue(Files.equal(asciiFile, asciiFile));

    File temp = createTempFile();
    Files.copy(asciiFile, temp);
    assertTrue(Files.equal(asciiFile, temp));

    Files.copy(i18nFile, temp);
    assertTrue(Files.equal(i18nFile, temp));

    Files.copy(asciiFile, temp);
    RandomAccessFile rf = new RandomAccessFile(temp, "rw");
    rf.writeByte(0);
    rf.close();
    assertEquals(asciiFile.length(), temp.length());
    assertFalse(Files.equal(asciiFile, temp));

    assertTrue(Files.asByteSource(asciiFile)
        .contentEquals(Files.asByteSource(asciiFile)));

    // 0-length files have special treatment (/proc, etc.)
    assertTrue(Files.equal(asciiFile, new BadLengthFile(asciiFile, 0)));
  }

  public void testNewReader() throws IOException {
    File asciiFile = getTestFile("ascii.txt");
    try {
      Files.newReader(asciiFile, null);
      fail("expected exception");
    } catch (NullPointerException expected) {
    }

    try {
      Files.newReader(null, Charsets.UTF_8);
      fail("expected exception");
    } catch (NullPointerException expected) {
    }

    BufferedReader r = Files.newReader(asciiFile, Charsets.US_ASCII);
    try {
      assertEquals(ASCII, r.readLine());
    } finally {
      r.close();
    }
  }

  public void testNewWriter() throws IOException {
    File temp = createTempFile();
    try {
      Files.newWriter(temp, null);
      fail("expected exception");
    } catch (NullPointerException expected) {
    }

    try {
      Files.newWriter(null, Charsets.UTF_8);
      fail("expected exception");
    } catch (NullPointerException expected) {
    }

    BufferedWriter w = Files.newWriter(temp, Charsets.UTF_8);
    try {
      w.write(I18N);
    } finally {
      w.close();
    }

    File i18nFile = getTestFile("i18n.txt");
    assertTrue(Files.equal(i18nFile, temp));
  }

  public void testTouch() throws IOException {
    File temp = createTempFile();
    assertTrue(temp.exists());
    assertTrue(temp.delete());
    assertFalse(temp.exists());
    Files.touch(temp);
    assertTrue(temp.exists());
    Files.touch(temp);
    assertTrue(temp.exists());

    try {
      Files.touch(new File(temp.getPath()) {
        @Override
        public boolean setLastModified(long t) {
          return false;
        }

        private static final long serialVersionUID = 0;
      });
      fail("expected exception");
    } catch (IOException expected) {
    }
  }

  public void testTouchTime() throws IOException {
    File temp = createTempFile();
    assertTrue(temp.exists());
    temp.setLastModified(0);
    assertEquals(0, temp.lastModified());
    Files.touch(temp);
    assertThat(temp.lastModified()).isNotEqualTo(0);
  }

  public void testCreateParentDirs_root() throws IOException {
    File file = root();
    assertNull(file.getParentFile());
    assertNull(file.getCanonicalFile().getParentFile());
    Files.createParentDirs(file);
  }

  public void testCreateParentDirs_relativePath() throws IOException {
    File file = file("nonexistent.file");
    assertNull(file.getParentFile());
    assertNotNull(file.getCanonicalFile().getParentFile());
    Files.createParentDirs(file);
  }

  public void testCreateParentDirs_noParentsNeeded() throws IOException {
    File file = file(getTempDir(), "nonexistent.file");
    assertTrue(file.getParentFile().exists());
    Files.createParentDirs(file);
  }

  public void testCreateParentDirs_oneParentNeeded() throws IOException {
    File file = file(getTempDir(), "parent", "nonexistent.file");
    File parent = file.getParentFile();
    assertFalse(parent.exists());
    try {
      Files.createParentDirs(file);
      assertTrue(parent.exists());
    } finally {
      assertTrue(parent.delete());
    }
  }

  public void testCreateParentDirs_multipleParentsNeeded() throws IOException {
    File file = file(getTempDir(), "grandparent", "parent", "nonexistent.file");
    File parent = file.getParentFile();
    File grandparent = parent.getParentFile();
    assertFalse(grandparent.exists());
    Files.createParentDirs(file);
    assertTrue(parent.exists());
  }

  public void testCreateParentDirs_nonDirectoryParentExists() throws IOException {
    File parent = getTestFile("ascii.txt");
    assertTrue(parent.isFile());
    File file = file(parent, "foo");
    try {
      Files.createParentDirs(file);
      fail();
    } catch (IOException expected) {
    }
  }

  public void testCreateTempDir() {
    File temp = Files.createTempDir();
    assertTrue(temp.exists());
    assertTrue(temp.isDirectory());
    assertThat(temp.listFiles()).isEmpty();
    assertTrue(temp.delete());
  }

  public void testMove() throws IOException {
    File i18nFile = getTestFile("i18n.txt");
    File temp1 = createTempFile();
    File temp2 = createTempFile();

    Files.copy(i18nFile, temp1);
    moveHelper(true, temp1, temp2);
    assertTrue(Files.equal(temp2, i18nFile));
  }

  public void testMoveViaCopy() throws IOException {
    File i18nFile = getTestFile("i18n.txt");
    File temp1 = createTempFile();
    File temp2 = createTempFile();

    Files.copy(i18nFile, temp1);
    moveHelper(true, new UnmovableFile(temp1, false, true), temp2);
    assertTrue(Files.equal(temp2, i18nFile));
  }

  public void testMoveFailures() throws IOException {
    File temp1 = createTempFile();
    File temp2 = createTempFile();

    moveHelper(false, new UnmovableFile(temp1, false, false), temp2);
    moveHelper(false, new UnmovableFile(temp1, false, false),
        new UnmovableFile(temp2, true, false));

    try {
      File asciiFile = getTestFile("ascii.txt");
      moveHelper(false, asciiFile, asciiFile);
      fail("expected exception");
    } catch (IllegalArgumentException expected) {
    }
  }

  private void moveHelper(boolean success, File from, File to)
      throws IOException {
    try {
      Files.move(from, to);
      if (success) {
        assertFalse(from.exists());
        assertTrue(to.exists());
      } else {
        fail("expected exception");
      }
    } catch (IOException possiblyExpected) {
      if (success) {
        throw possiblyExpected;
      }
    }
  }

  private static class UnmovableFile extends File {

    private final boolean canRename;
    private final boolean canDelete;

    public UnmovableFile(File file, boolean canRename, boolean canDelete) {
      super(file.getPath());
      this.canRename = canRename;
      this.canDelete = canDelete;
    }

    @Override
    public boolean renameTo(File to) {
      return canRename && super.renameTo(to);
    }

    @Override
    public boolean delete() {
      return canDelete && super.delete();
    }

    private static final long serialVersionUID = 0;
  }

  public void testLineReading() throws IOException {
    File temp = createTempFile();
    assertNull(Files.readFirstLine(temp, Charsets.UTF_8));
    assertTrue(Files.readLines(temp, Charsets.UTF_8).isEmpty());

    PrintWriter w = new PrintWriter(Files.newWriter(temp, Charsets.UTF_8));
    w.println("hello");
    w.println("");
    w.println(" world  ");
    w.println("");
    w.close();

    assertEquals("hello", Files.readFirstLine(temp, Charsets.UTF_8));
    assertEquals(ImmutableList.of("hello", "", " world  ", ""),
        Files.readLines(temp, Charsets.UTF_8));

    assertTrue(temp.delete());
  }

  public void testReadLines_withLineProcessor() throws IOException {
    File temp = createTempFile();
    LineProcessor<List collect = new LineProcessor>() {
      List<String> collector = new ArrayList();

      @Override
      public boolean processLine(String line) {
        collector.add(line);
        return true;
      }

      @Override
      public List<String> getResult() {
        return collector;
      }
    };
    assertThat(Files.readLines(temp, Charsets.UTF_8, collect)).isEmpty();

    PrintWriter w = new PrintWriter(Files.newWriter(temp, Charsets.UTF_8));
    w.println("hello");
    w.println("");
    w.println(" world  ");
    w.println("");
    w.close();
    Files.readLines(temp, Charsets.UTF_8, collect);
    assertThat(collect.getResult())
        .containsExactly("hello", "", " world  ", "").inOrder();

    LineProcessor<List collectNonEmptyLines =
        new LineProcessor<List() {
          List<String> collector = new ArrayList();

          @Override
          public boolean processLine(String line) {
            if (line.length() > 0) {
              collector.add(line);
            }
            return true;
          }

          @Override
          public List<String> getResult() {
            return collector;
          }
        };
    Files.readLines(temp, Charsets.UTF_8, collectNonEmptyLines);
    assertThat(collectNonEmptyLines.getResult()).containsExactly(
        "hello", " world  ").inOrder();

    assertTrue(temp.delete());
  }

  public void testHash() throws IOException {
    File asciiFile = getTestFile("ascii.txt");
    File i18nFile = getTestFile("i18n.txt");

    String init = "d41d8cd98f00b204e9800998ecf8427e";
    assertEquals(init, Hashing.md5().newHasher().hash().toString());

    String asciiHash = "e5df5a39f2b8cb71b24e1d8038f93131";
    assertEquals(asciiHash, Files.hash(asciiFile, Hashing.md5()).toString());

    String i18nHash = "7fa826962ce2079c8334cd4ebf33aea4";
    assertEquals(i18nHash, Files.hash(i18nFile, Hashing.md5()).toString());
  }

  public void testMap() throws IOException {
    // Test data
    int size = 1024;
    byte[] bytes = newPreFilledByteArray(size);

    // Setup
    File file = createTempFile();
    Files.write(bytes, file);

    // Test
    MappedByteBuffer actual = Files.map(file);

    // Verify
    ByteBuffer expected = ByteBuffer.wrap(bytes);
    assertTrue("ByteBuffers should be equal.", expected.equals(actual));
  }

  public void testMap_noSuchFile() throws IOException {
    // Setup
    File file = createTempFile();
    boolean deleted = file.delete();
    assertTrue(deleted);

    // Test
    try {
      Files.map(file);
      fail("Should have thrown FileNotFoundException.");
    } catch (FileNotFoundException expected) {
    }
  }

  public void testMap_readWrite() throws IOException {
    // Test data
    int size = 1024;
    byte[] expectedBytes = new byte[size];
    byte[] bytes = newPreFilledByteArray(1024);

    // Setup
    File file = createTempFile();
    Files.write(bytes, file);

    Random random = new Random();
    random.nextBytes(expectedBytes);

    // Test
    MappedByteBuffer map = Files.map(file, MapMode.READ_WRITE);
    map.put(expectedBytes);

    // Verify
    byte[] actualBytes = Files.toByteArray(file);
    assertTrue(Arrays.equals(expectedBytes, actualBytes));
  }

  public void testMap_readWrite_creates() throws IOException {
    // Test data
    int size = 1024;
    byte[] expectedBytes = newPreFilledByteArray(1024);

    // Setup
    File file = createTempFile();
    boolean deleted = file.delete();
    assertTrue(deleted);
    assertFalse(file.exists());

    // Test
    MappedByteBuffer map = Files.map(file, MapMode.READ_WRITE, size);
    map.put(expectedBytes);

    // Verify
    assertTrue(file.exists());
    assertTrue(file.isFile());
    assertEquals(size, file.length());
    byte[] actualBytes = Files.toByteArray(file);
    assertTrue(Arrays.equals(expectedBytes, actualBytes));
  }

  public void testMap_readWrite_max_value_plus_1() throws IOException {
    // Setup
    File file = createTempFile();
    // Test
    try {
      Files.map(file, MapMode.READ_WRITE, (long) Integer.MAX_VALUE + 1);
      fail("Should throw when size exceeds Integer.MAX_VALUE");
    } catch (IllegalArgumentException expected) {
    }
  }

  public void testGetFileExtension() {
    assertEquals("txt", Files.getFileExtension(".txt"));
    assertEquals("txt", Files.getFileExtension("blah.txt"));
    assertEquals("txt", Files.getFileExtension("blah..txt"));
    assertEquals("txt", Files.getFileExtension(".blah.txt"));
    assertEquals("txt", Files.getFileExtension("/tmp/blah.txt"));
    assertEquals("gz", Files.getFileExtension("blah.tar.gz"));
    assertEquals("", Files.getFileExtension("/"));
    assertEquals("", Files.getFileExtension("."));
    assertEquals("", Files.getFileExtension(".."));
    assertEquals("", Files.getFileExtension("..."));
    assertEquals("", Files.getFileExtension("blah"));
    assertEquals("", Files.getFileExtension("blah."));
    assertEquals("", Files.getFileExtension(".blah."));
    assertEquals("", Files.getFileExtension("/foo.bar/blah"));
    assertEquals("", Files.getFileExtension("/foo/.bar/blah"));
  }

  public void testGetNameWithoutExtension() {
    assertEquals("", Files.getNameWithoutExtension(".txt"));
    assertEquals("blah", Files.getNameWithoutExtension("blah.txt"));
    assertEquals("blah.", Files.getNameWithoutExtension("blah..txt"));
    assertEquals(".blah", Files.getNameWithoutExtension(".blah.txt"));
    assertEquals("blah", Files.getNameWithoutExtension("/tmp/blah.txt"));
    assertEquals("blah.tar", Files.getNameWithoutExtension("blah.tar.gz"));
    assertEquals("", Files.getNameWithoutExtension("/"));
    assertEquals("", Files.getNameWithoutExtension("."));
    assertEquals(".", Files.getNameWithoutExtension(".."));
    assertEquals("..", Files.getNameWithoutExtension("..."));
    assertEquals("blah", Files.getNameWithoutExtension("blah"));
    assertEquals("blah", Files.getNameWithoutExtension("blah."));
    assertEquals(".blah", Files.getNameWithoutExtension(".blah."));
    assertEquals("blah", Files.getNameWithoutExtension("/foo.bar/blah"));
    assertEquals("blah", Files.getNameWithoutExtension("/foo/.bar/blah"));
  }

  public void testReadBytes() throws IOException {
    ByteProcessor<byte[]> processor = new ByteProcessor() {
      private final ByteArrayOutputStream out = new ByteArrayOutputStream();

      @Override
      public boolean processBytes(byte[] buffer, int offset, int length) throws IOException {
        if (length >= 0) {
          out.write(buffer, offset, length);
        }
        return true;
      }

      @Override
      public byte[] getResult() {
        return out.toByteArray();
      }
    };

    File asciiFile = getTestFile("ascii.txt");
    byte[] result = Files.readBytes(asciiFile, processor);
    assertEquals(Bytes.asList(Files.toByteArray(asciiFile)), Bytes.asList(result));
  }

  public void testReadBytes_returnFalse() throws IOException {
    ByteProcessor<byte[]> processor = new ByteProcessor() {
      private final ByteArrayOutputStream out = new ByteArrayOutputStream();

      @Override
      public boolean processBytes(byte[] buffer, int offset, int length) throws IOException {
        if (length > 0) {
          out.write(buffer, offset, 1);
          return false;
        } else {
          return true;
        }
      }

      @Override
      public byte[] getResult() {
        return out.toByteArray();
      }
    };

    File asciiFile = getTestFile("ascii.txt");
    byte[] result = Files.readBytes(asciiFile, processor);
    assertEquals(1, result.length);
  }

  public void testPredicates() throws IOException {
    File asciiFile = getTestFile("ascii.txt");
    File dir = asciiFile.getParentFile();
    assertTrue(Files.isDirectory().apply(dir));
    assertFalse(Files.isFile().apply(dir));

    assertFalse(Files.isDirectory().apply(asciiFile));
    assertTrue(Files.isFile().apply(asciiFile));
  }

  /**
   * Returns a root path for the file system.
   */
  private static File root() {
    return File.listRoots()[0];
  }

  /**
   * Returns a {@code File} object for the given path parts.
   */
  private static File file(String first, String... more) {
    return file(new File(first), more);
  }

  /**
   * Returns a {@code File} object for the given path parts.
   */
  private static File file(File first, String... more) {
    // not very efficient, but should definitely be correct
    File file = first;
    for (String name : more) {
      file = new File(file, name);
    }
    return file;
  }
}