What causes "%s" in junit-team/junit5?

Inspect the wrapped NamespacedHierarchicalStoreException message - it states the actual constraint violated.

junit-team/junit5 · error · ExtensionContextException

%s

Error message

%s

What it means

A generic wrapper thrown by NamespaceAwareStore.accessStore: any operation on the ExtensionContext.Store (get, put, getOrComputeIfAbsent, remove, computeIfAbsent, etc.) that fails inside the underlying NamespacedHierarchicalStore with a NamespacedHierarchicalStoreException is rethrown as an ExtensionContextException carrying the same message. The '%s' message is whatever the store layer produced (type mismatch, null key, etc.).

Source

Thrown at junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/execution/NamespaceAwareStore.java:123

		Preconditions.notNull(key, "key must not be null");
		Supplier<@Nullable Object> action = () -> this.valuesStore.remove(this.namespace, key);
		return this.<@Nullable Object> accessStore(action);
	}

	@Override
	public <T> @Nullable T remove(Object key, Class<T> requiredType) {
		Preconditions.notNull(key, "key must not be null");
		Preconditions.notNull(requiredType, "requiredType must not be null");
		Supplier<@Nullable T> action = () -> this.valuesStore.remove(this.namespace, key, requiredType);
		return this.<@Nullable T> accessStore(action);
	}

	private <T extends @Nullable Object> T accessStore(Supplier<T> action) {
		try {
			return action.get();
		}
		catch (NamespacedHierarchicalStoreException e) {
			throw new ExtensionContextException(e.getMessage(), e);
		}
	}

}

View on GitHub (pinned to f070c699a0)

Solutions

Inspect the wrapped NamespacedHierarchicalStoreException message - it states the actual constraint violated.
Use a consistent type per (namespace, key) pair across all extensions sharing the namespace.
Avoid sharing mutable stored objects across parallel test threads without external synchronization.

Example fix

// before
store.put("cfg", List.of("a"));
Map<String,String> cfg = store.get("cfg", Map.class); // type mismatch -> wrapped
// after
store.put("cfg", Map.of("k","v"));
Map<String,String> cfg = store.get("cfg", Map.class);

Defensive patterns

Strategy: try-catch

Validate before calling

Object stored = store.get(key);
Class<?> expected = Map.class;
if (stored != null && !expected.isInstance(stored)) {
    throw new IllegalStateException("Stored " + stored.getClass() + " is not " + expected);
}

Type guard

Object v = store.get("cfg");
if (!(v instanceof Map<?,?> m)) {
    throw new IllegalStateException("expected Map, got " + (v == null ? "null" : v.getClass()));
}

Try / catch

try {
    Map<String,String> cfg = store.get("cfg", Map.class);
} catch (ExtensionContextException e) {
    log.error("store access failed: {}", e.getCause());
    throw e;
}

Prevention

Use a single type per (namespace, key) pair across extensions.
Prefer typed accessors get(key, requiredType) over raw get(key) plus casts.
Avoid sharing mutable stored objects across parallel test threads without synchronization.

When it happens

Trigger: Any Store.<operation> where the underlying store throws - e.g. get(key, requiredType) with a stored value that is not assignable to requiredType, or computeIfAbsent racing on a null defaultCreator result. accessStore catches NamespacedHierarchicalStoreException and wraps it.

Common situations: Storing mixed types under the same key and later fetching with the wrong requiredType; one extension stores a List and another fetches with Map.class; concurrent modification of the store from parallel test threads when the store is not thread-safe for the operation.

Related errors

AI-assisted analysis of junit-team/junit5@f070c699a0 (2026-08-11). Data as JSON: /api/errors/97163674993c587e. Report an issue: GitHub.