junit-team/junit5 · error · ExtensionConfigurationException

@DefaultLocale not configured correctly. When not using a la

Error message

@DefaultLocale not configured correctly. When not using a language tag, specify either language, or language and country, or language and country and variant.

What it means

Thrown as ExtensionConfigurationException by DefaultLocaleExtension.createFromParts when parts-based @DefaultLocale configuration is internally inconsistent: language is set but country is empty and variant is non-empty. The only valid parts-based shapes are language alone, language+country, or language+country+variant — variant without country is not a legal Locale.

Source

Thrown at junit-jupiter-api/src/main/java/org/junit/jupiter/api/util/DefaultLocaleExtension.java:96

	private static Locale createFromParts(DefaultLocale annotation) {
		if (annotation.localeProvider() != NullLocaleProvider.class)
			throw new ExtensionConfigurationException(
				"@DefaultLocale can only be used with language tag if provider is not set");
		String language = annotation.language();
		String country = annotation.country();
		String variant = annotation.variant();
		if (!language.isEmpty() && !country.isEmpty() && !variant.isEmpty()) {
			return JupiterLocaleUtils.createLocale(language, country, variant);
		}
		else if (!language.isEmpty() && !country.isEmpty()) {
			return JupiterLocaleUtils.createLocale(language, country);
		}
		else if (!language.isEmpty() && variant.isEmpty()) {
			return JupiterLocaleUtils.createLocale(language);
		}
		else {
			throw new ExtensionConfigurationException(
				"@DefaultLocale not configured correctly. When not using a language tag, specify either"
						+ " language, or language and country, or language and country and variant.");
		}
	}

	private static Locale getFromProvider(DefaultLocale annotation) {
		if (!annotation.country().isEmpty() || !annotation.variant().isEmpty())
			throw new ExtensionConfigurationException(
				"@DefaultLocale can only be used with a provider if value, language, country and variant are not set.");
		var providerClass = annotation.localeProvider();
		LocaleProvider provider;
		try {
			provider = ReflectionSupport.newInstance(providerClass);
		}
		catch (Exception exception) {
			throw new ExtensionConfigurationException(
				"LocaleProvider instance could not be constructed because of an exception", exception);
		}

View on GitHub (pinned to 956246301e)

Solutions

Add the missing country attribute: @DefaultLocale(language = "en", country = "US", variant = "POSIX").
If you did not intend a variant, remove variant= and use language alone or language+country.
Prefer the BCP-47 tag form @DefaultLocale(value = "en-US-POSIX") which lets Locale.forLanguageTag normalize the parts.

Example fix

// before
@DefaultLocale(language = "en", variant = "POSIX")
void test() {}

// after — variant requires a country
@DefaultLocale(language = "en", country = "US", variant = "POSIX")
void test() {}

Defensive patterns

Strategy: validation

Validate before calling

DefaultLocale d = testClass.getAnnotation(DefaultLocale.class);
boolean l = !d.language().isEmpty(), c = !d.country().isEmpty(), v = !d.variant().isEmpty();
boolean validParts = l || c || v
    ? (l && !v) || (l && c) // language alone, language+country[+variant]
    : true;
if (!validParts) {
    throw new IllegalStateException("@DefaultLocale parts require language, and variant requires country");
}

Prevention

Variant requires country; country requires language. The only valid stacks are L, L+C, L+C+V.
Prefer @DefaultLocale(value = "en-US-POSIX") to let the JVM normalize parts for you.
Double-check trimmed-down @DefaultLocale annotations to ensure no orphan variant= or country=.

When it happens

Trigger: Annotating a test with @DefaultLocale(language = "en", variant = "POSIX") (no country). Also reached if country is somehow empty while variant is set, regardless of which attribute the developer thought they were configuring.

Common situations: Misunderstanding the Locale(language, country, variant) constructor contract (variant requires country); trimming a @DefaultLocale down and accidentally removing country= but leaving variant=.

Related errors

AI-assisted analysis of junit-team/junit5@956246301e (2026-08-04). Data as JSON: /data/errors/933d2eb922832bed.json. Report an issue: GitHub.