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

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 own implementation.

I asked Google to provide first-party support in google/jimfs#258. However, Google has not yet started using JUnit Jupiter and first-party support may only be provided when Google does so.

For this reason, I decided to implement this extension to aid all the users that would like a smooth integration between Jimfs and JUnit Jupiter. If Google ever offers first-party support for this integration, this project will likely be discontinued.

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.

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

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

The simplest possible 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 operating system.

Note that only annotated fields or parameters of type Path are supported as Jimfs is a non-default file system, and File instances are associated with the default file system only.

@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 operating system.

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:

• FOR_CURRENT_PLATFORM: appropriate to the current operating system (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 operating system the test is running on:

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

The junit.jupiter.tempdir.factory.default configuration parameter can be used to specify the fully qualified class name of the factory to be used by default. 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.

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!

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