### Question:
PaymentConfiguration { @NonNull public static PaymentConfiguration getInstance() { if (mInstance == null) { throw new IllegalStateException( "Attempted to get instance of PaymentConfiguration without initialization."); } return mInstance; } private  PaymentConfiguration(@NonNull String publishableKey); @NonNull static PaymentConfiguration getInstance(); static void init(@NonNull String publishableKey); @NonNull String getPublishableKey(); @Address.RequiredBillingAddressFields int getRequiredBillingAddressFields(); @NonNull PaymentConfiguration setRequiredBillingAddressFields(
            @Address.RequiredBillingAddressFields int requiredBillingAddressFields); boolean getShouldUseSourcesForCards(); @NonNull PaymentConfiguration setShouldUseSourcesForCards(boolean shouldUseSourcesForCards);  }### Answer:
@Test(expected = IllegalStateException.class) public void getInstance_beforeInit_throwsRuntimeException() { PaymentConfiguration.getInstance(); fail("Should not be able to get a payment configuration before it has been initialized."); }