junit-team/junit5 · error · PreconditionViolationException

temp directory with non-default file system cannot be inject

Error message

temp directory with non-default file system cannot be injected into java.io.File target

What it means

Thrown by CloseablePath's constructor when the TempDirFactory returns a Path whose FileSystem is not the default filesystem, but the injection target type is java.io.File. java.io.File can only represent paths on the default filesystem, so converting a non-default Path to File would be lossy/incorrect; the constructor rejects it as a PreconditionViolationException after closing the factory.

Source

Thrown at junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TempDirectory.java:278

		private final AnnotatedElementContext elementContext;
		private final ExtensionContext extensionContext;

		private CloseablePath(TempDirFactory factory, Cleanup cleanup, Class<?> elementType,
				AnnotatedElementContext elementContext, ExtensionContext extensionContext) throws Exception {
			this.dir = factory.createTempDirectory(elementContext, extensionContext);
			this.factory = factory;
			this.cleanup = cleanup;
			this.elementContext = elementContext;
			this.extensionContext = extensionContext;

			if (this.dir == null || !Files.isDirectory(this.dir)) {
				close();
				throw new PreconditionViolationException("temp directory must be a directory");
			}

			if (elementType == File.class && !this.dir.getFileSystem().equals(FileSystems.getDefault())) {
				close();
				throw new PreconditionViolationException(
					"temp directory with non-default file system cannot be injected into " + File.class.getName()
							+ " target");
			}
		}

		Path get() {
			return requireNonNull(this.dir);
		}

		@Override
		public void close() throws IOException {
			try {
				if (this.dir != null) {
					this.cleanup.run(this.dir, this.elementContext, this.extensionContext);
				}
			}
			finally {
				this.factory.close();

View on GitHub (pinned to 956246301e)

Solutions

1. Change the @TempDir field/parameter type from java.io.File to java.nio.file.Path so a non-default filesystem is supported.
2. Or make the custom TempDirFactory create the directory on the default filesystem (FileSystems.getDefault()) if a File target is required.

Example fix

// before
@TempDir(factory = JimfsFactory.class)
File tmp; // Jimfs path is non-default fs -> PreconditionViolationException

// after
@TempDir(factory = JimfsFactory.class)
java.nio.file.Path tmp; // Path supports any FileSystem

// If using a non-default-fs factory, force the target type to Path
if (usesCustomFileSystem(factory) && targetType == File.class) {
    throw new IllegalStateException("Use Path, not File, with a non-default filesystem factory");
}

static boolean targetMatchesFileSystem(Class<?> targetType, Path sample) {
    return targetType == java.nio.file.Path.class
        || java.nio.file.FileSystems.getDefault().equals(sample.getFileSystem());
}

When it happens

Trigger: Using a custom @TempDir(factory = ...) that returns a Path from a custom FileSystem (e.g. Jimfs in-memory filesystem, zip filesystem), while declaring the @TempDir field/parameter as java.io.File rather than java.nio.file.Path.

Common situations: In-memory filesystem testing libraries (Jimfs) wired as a TempDirFactory, with a test field accidentally typed as File; refactoring a Path-based test to File while keeping a custom factory that produces non-default-fs paths.

Related errors

• Can only resolve @TempDir <target> of type java.nio.file.Pat
• Failed to create default temp directory
• temp directory must be a directory
• TestInstanceFactory [%s] failed to return an instance of [%s
• @TempDir field [<field>] must not be declared as final.

AI-assisted analysis of junit-team/junit5@956246301e (2026-08-04). Data as JSON: /data/errors/f0566d82f510cf42.json. Report an issue: GitHub.