@Test
public void singleProductMissingInCart() throws Exception {

    requiredProductsInCart("900901", "900902", "900903", "900904");
    RegisterNew command = givenCartRegistrationCommand("900902", "900903", "900904");
    ValidationResult result = validator.validate(command);
    Assertions.assertThat(result.getViolations())
            .contains("refNo 900901 expected in pocket 1, but not found");
}