Jimfs JUnit Jupiter

This project provides a JUnit Jupiter extension for in-memory @TempDir directories via the Jimfs file system.

Motivation

Today, it is already possible to use Jimfs and JUnit Jupiter together to create in-memory temporary directories for testing. However, it requires Jimfs in-memory file system handling hooked into JUnit Jupiter test lifecycle callbacks, a boilerplate that users must implement on their own.

Starting from version 5.10, JUnit Jupiter offers a TempDirFactory SPI for customizing how temporary directories are created via the @TempDir annotation. The SPI allows libraries like Jimfs to provide their implementation.

First-party support was requested in google/jimfs#258. However, Google has not yet started using JUnit Jupiter, and such first-party support may only be provided when Google does so.

Because of that, this extension was created to aid all the users who would like a smooth integration between Jimfs and JUnit Jupiter. This project will likely be discontinued if Google ever offers first-party support for this integration.

Compatibility

Jimfs JUnit Jupiter is based on JUnit Jupiter 5, thus requiring at least Java 8.

Compatibility is guaranteed only with the JUnit Jupiter versions from 5.10 to the latest.

Getting Started

Maven

<dependency>
  <groupId>io.github.scordio</groupId>
  <artifactId>jimfs-junit-jupiter</artifactId>
  <version>${jimfs-junit-jupiter.version}</version>
  <scope>test</scope>
</dependency>

Gradle

testImplementation("io.github.scordio:jimfs-junit-jupiter:${jimfsJunitJupiterVersion}")

JimfsTempDirFactory

The simplest usage is to set the factory attribute of @TempDir to JimfsTempDirFactory:

@Test
void test(@TempDir(factory = JimfsTempDirFactory.class) Path tempDir) {
  assertThat(tempDir.getFileSystem().provider().getScheme()).isEqualTo("jimfs");
}

tempDir is resolved into an in-memory temporary directory based on Jimfs, appropriately configured for the current platform.

@JimfsTempDir

@JimfsTempDir, a @TempDir composed annotation, can be used as a drop-in replacement for @TempDir(factory = JimfsTempDirFactory.class):

@Test
void test(@JimfsTempDir Path tempDir) {
  assertThat(tempDir.getFileSystem().provider().getScheme()).isEqualTo("jimfs");
}

The default behavior of the annotation is equivalent to using JimfsTempDirFactory directly: tempDir is resolved into an in-memory temporary directory based on Jimfs, appropriately configured for the current platform.

For better control over the underlying in-memory file system, @JimfsTempDir offers an optional value attribute that can be set to the desired configuration, one of:

• DEFAULT: based on the corresponding configuration parameter (default)
• FOR_CURRENT_PLATFORM: appropriate to the current platform
• OS_X: for a Mac OS X-like file system
• UNIX: for a UNIX-like file system
• WINDOWS: for a Windows-like file system

For example, the following defines a Windows-like temporary directory regardless of the platform the test is running on:

@Test
void test(@JimfsTempDir(WINDOWS) Path tempDir) {
  assertThat(tempDir.getFileSystem().getSeparator()).isEqualTo("\\");
}

Configuration Parameters

Jimfs JUnit Jupiter supports JUnit configuration parameters.

Default @TempDir Factory

The junit.jupiter.tempdir.factory.default configuration parameter sets the default factory to use, expecting its fully qualified class name.

For example, the following configures JimfsTempDirFactory:

junit.jupiter.tempdir.factory.default=io.github.scordio.jimfs.junit.jupiter.JimfsTempDirFactory

The factory will be used for all @TempDir annotations unless the factory attribute of the annotation specifies a different type.

Default Jimfs Configuration

The jimfs.junit.jupiter.tempdir.configuration.default configuration parameter sets the default Jimfs configuration to use, expecting one of the following (case-insensitive):

• FOR_CURRENT_PLATFORM: appropriate to the current platform (default)
• OS_X: for a Mac OS X-like file system
• UNIX: for a UNIX-like file system
• WINDOWS: for a Windows-like file system

For example, the following defines a Windows-like temporary directory regardless of the platform the test is running on:

jimfs.junit.jupiter.tempdir.configuration.default=windows

All Jimfs-based temporary directories will be configured accordingly unless @JimfsTempDir is used and its value attribute is set.

Limitations

Jimfs JUnit Jupiter only supports annotated fields or parameters of type Path, as Jimfs is a non-default file system and File instances can only be associated with the default file system.

Improvements

Compared to the configuration options that Jimfs provides, Jimfs JUnit Jupiter exposes a much smaller surface to keep its usage simple.

In case something is missing for your use case, please raise an issue!

License

Jimfs JUnit Jupiter is released under version 2.0 of the Apache License.