MockFs

About

Java FileSystem for simulating IOExceptions

Usage

1. Add maven dependency:

<dependency>
  <groupId>com.aerse</groupId>
  <artifactId>mockfs</artifactId>
  <version>1.4</version>
</dependency>

2. Ensure code is ready

• Ensure java.nio.file.Path is used instead of java.io.File. FileSystem is available only for Path.
• Ensure Path::resolve(...) is used instead of java.nio.file.Paths.get(...) or Path::of(...). The latter uses FileSystems.getDefault() instead of mocked
• All Path should be created from the FileSystem using FileSystem::getPath(...) method.

3. Setup the test

For example:

	@Test(expected = IOException.class)
	public void testFailingWrite() throws IOException {
		byte[] data = createSampleData();
		Path path = basePath.resolve(UUID.randomUUID().toString());
		mockFs.mock(path, new FailingByteChannelCallback(5));
		try (OutputStream w = Files.newOutputStream(path)) {
			w.write(data);
		}
	}

Features

• MockFileSystem could transparently pass the data to the default FileSystem. Just use com.aerse.mockfs.NoOpByteChannelCallback:

   	FileSystem fs = FileSystems.getDefault();
   	MockFileSystem mockFs = new MockFileSystem(fs);
   	mockFs.mock(path, new NoOpByteChannelCallback());

• Use com.aerse.mockfs.FailingByteChannelCallback for simulating IOExceptions after configurable number of bytes.
• Mock read/write to every file in the directory. Just pass this directory to the com.aerse.mockfs.MockFileSystem::mock(directoryToMock, ...)