code: package usecases;
  
  import java.io.IOException;
  import java.nio.file.AccessDeniedException;
  import java.nio.file.Files;
  import java.nio.file.Path;
  
  import com.beijunyi.parallelgit.filesystem.AbstractGitFileSystemTest;
  import com.beijunyi.parallelgit.filesystem.GitPath;
  import org.junit.Test;
  
  import static org.junit.Assert.*;
  
  public class FilesWriteTest extends AbstractGitFileSystemTest {
  
    @Test
    public void writeExistingFile_shouldOverwriteItsContent() throws IOException {
      initRepository();
      writeToCache("/file.txt", "old content");
      commitToMaster();
      initGitFileSystem();
      byte[] data =someBytes();
      Path file = gfs.getPath("/file.txt");
      Files.write(file, data);
      assertArrayEquals(data, Files.readAllBytes(file));
    }
  
    @Test
    public void writeNonExistentFile_shouldCreateNewFile() throws IOException {
      initGitFileSystem();
      GitPath file = gfs.getPath("/file.txt");
      Files.write(file, someBytes());
      assertTrue(Files.exists(file));
    }
  
    @Test(expected = AccessDeniedException.class)
    public void writeDirectory_shouldThrowAccessDeniedException() throws IOException {
      initRepository();
      writeToCache("/dir/file.txt");
      commitToMaster();
      initGitFileSystem();
      GitPath dir = gfs.getPath("/dir");
      Files.write(dir, someBytes());
    }
  
    @Test(expected = AccessDeniedException.class)
    public void writeRoot_shouldThrowAccessDeniedException() throws IOException {
      initGitFileSystem();
      Files.write(root, someBytes());
    }
  
  
  
  
  }
  