junit-team/junit5 · error · ExtensionConfigurationException

@DefaultLocale can only be used with a provider if value, la

Error message

@DefaultLocale can only be used with a provider if value, language, country and variant are not set.

What it means

Thrown as ExtensionConfigurationException by DefaultLocaleExtension.getFromProvider when @DefaultLocale is in provider mode (value and language empty) but country= or variant= is set. The provider is the sole source of the Locale; country and variant must not be combined with it.

Source

Thrown at junit-jupiter-api/src/main/java/org/junit/jupiter/api/util/DefaultLocaleExtension.java:104

		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);
		}
		return invoke(provider);
	}

	@SuppressWarnings("ConstantValue")
	private static Locale invoke(LocaleProvider provider) {
		var locale = provider.get();
		if (locale == null) {
			throw new ExtensionConfigurationException("LocaleProvider instance returned with null");

View on GitHub (pinned to 956246301e)

Solutions

1. Remove country= and variant= when using localeProvider=; let the provider return the full Locale.
2. If you need specific parts, switch to parts-based mode (language=/country=/variant=) and remove localeProvider=.

Example fix

// before
@DefaultLocale(country = "US", localeProvider = MyLocaleProvider.class)
void test() {}

// after — provider mode is exclusive
@DefaultLocale(localeProvider = MyLocaleProvider.class)
void test() {}

DefaultLocale d = testClass.getAnnotation(DefaultLocale.class);
boolean providerMode = d.value().isEmpty() && d.language().isEmpty();
boolean providerSet = d.localeProvider() != NullLocaleProvider.class;
if (providerMode && providerSet && (!d.country().isEmpty() || !d.variant().isEmpty())) {
    throw new IllegalStateException("@DefaultLocale provider cannot be combined with country= or variant=");
}

When it happens

Trigger: Annotating a test with @DefaultLocale(country = "US", localeProvider = MyProvider.class) or @DefaultLocale(variant = "POSIX", localeProvider = MyProvider.class) without setting value or language.

Common situations: Trying to 'augment' a provider-supplied Locale with extra parts; partial migration where country= was left behind when switching to provider mode.

Related errors

• @DefaultLocale can only be used with language tag if languag
• @DefaultLocale can only be used with language tag if provide
• @DefaultLocale not configured correctly. When not using a la
• LocaleProvider instance could not be constructed because of
• LocaleProvider instance returned with null

AI-assisted analysis of junit-team/junit5@956246301e (2026-08-04). Data as JSON: /data/errors/eedcce7995afef20.json. Report an issue: GitHub.