junit-team/junit5 · error · JUnitException

Failed to read contents of

Error message

Failed to read contents of ${reference}.

What it means

JUnitException thrown by ModuleReferenceClassScanner.scan when ModuleReader.open() or reader.list() raises IOException while scanning a JPMS module for classes. The offending ModuleReference is in the message and the IOException is the cause.

Solutions

1. Verify the module artifact opens cleanly: `jar tf <module>.jar` or `unzip -l`
2. Rebuild the offending modular jar
3. Check module-path permissions and storage reliability
4. Move the artifact to local disk if scanning a remote mount

try {
    // module classpath scanning
} catch (JUnitException e) {
    if (e.getCause() instanceof IOException io) {
        // inspect the module reference, repair the module path
    }
}

When it happens

Trigger: JPMS module classpath scanning where reading the module's contents fails - corrupt modular jar, broken module-path entry, IO error, or permission denial on the module artifact.

Common situations: Running tests on the module path (--module-path) with a corrupt or unreadable module; modular jar built incorrectly; module path pointing at a network resource that drops mid-scan.

Related errors

• Failed to close file system for
• Failed to create file system for
• Failed to load class with name
• Failed to load resource with name
• Error redirecting stderr to file

AI-assisted analysis of junit-team/junit5@f070c699a0 (2026-08-11). Data as JSON: /api/errors/176a62bc970b5573. Report an issue: GitHub.

Appendix: source

Thrown at junit-platform-commons/src/main/java/org/junit/platform/commons/util/ModuleUtils.java:269

		 * Scan module reference for classes that potentially contain testable methods.
		 */
		List<Class<?>> scan(ModuleReference reference) {
			try (ModuleReader reader = reference.open()) {
				try (Stream<String> names = reader.list()) {
					// @formatter:off
					return names.filter(name -> !name.endsWith("/")) // remove directories
							.map(Path::of)
							.filter(SearchPathUtils::isClassOrSourceFile)
							.map(SearchPathUtils::determineFullyQualifiedClassName)
							.filter(classFilter::match)
							.<Class<?>> map(this::loadClassUnchecked)
							.filter(classFilter::match)
							.toList();
					// @formatter:on
				}
			}
			catch (IOException e) {
				throw new JUnitException("Failed to read contents of " + reference + ".", e);
			}
		}

		/**
		 * Load class by its binary name.
		 *
		 * @see ClassLoader#loadClass(String)
		 */
		private Class<?> loadClassUnchecked(String binaryName) {
			try {
				return classLoader.loadClass(binaryName);
			}
			catch (ClassNotFoundException e) {
				throw new JUnitException("Failed to load class with name '" + binaryName + "'.", e);
			}
		}

	}

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