A test rule for setting device locale

ForceLocaleRule.java

public class ForceLocaleRule implements TestRule {

    private final Locale mTestLocale;
    private Locale mDeviceLocale;

    public ForceLocaleRule(Locale testLocale) {
        mTestLocale = testLocale;
    }

    @Override
    public Statement apply(Statement base, Description description) {
        return new Statement() {
            public void evaluate() throws Throwable {
                try {
                    if (mTestLocale != null) {
                        mDeviceLocale = Locale.getDefault();
                        setLocale(mTestLocale);
                    }

                    base.evaluate();
                } finally {
                    if (mDeviceLocale != null) {
                        setLocale(mDeviceLocale);
                    }
                }
            }
        };
    }


    public void setLocale(Locale locale) {
        Resources resources = InstrumentationRegistry.getTargetContext().getResources();
        Locale.setDefault(locale);
        Configuration config = resources.getConfiguration();
        config.locale = locale;
        resources.updateConfiguration(config, resources.getDisplayMetrics());
    }
}