SonarQube issue "Add at least one assertion to this test case" for unit test with assertions?

I'm having issues with SonarQube raising issues with several of my unit tests, prompting the following issue:

Add at least one assertion to this test case.

Each test case resembles this format (where a number of assertions are delegated to a method with common assertions, to avoid duplication):

@Test
public void companyNameOneTooLong() throws Exception {
    AddressFormBean formBean = getValidBean();
    formBean.setCompanyNameOne("123456789012345678901234567890123456");

    assertViolation(validator.validate(formBean), "companyNameOne", "length must be between 0 and 35");
}

private void assertViolation(Set<ConstraintViolation<AddressFormBean>> violations, String fieldname, String message) {
    assertThat(violations, hasSize(1));
    assertEquals(fieldname, violations.iterator().next().getPropertyPath().iterator().next().getName());
    assertEquals(message, violations.iterator().next().getMessage());
}

Now, obviously I could just pull the three assertions out of the private method and put them in the test method - but I'm performing the same checks (on different fields) multiple times.

So, I thought I'd try to emulate the behaviour of the assertion methods, by (re) throwing an AssertionError:

private void assertViolation(Set<ConstraintViolation<AddressFormBean>> violations, String fieldname, String message) throws AssertionError {
    try {
        assertThat(violations, hasSize(1));
        assertEquals(fieldname, violations.iterator().next().getPropertyPath().iterator().next().getName());
        assertEquals(message, violations.iterator().next().getMessage());
    } catch (AssertionError e) {
        throw e;
    }
 }

Unfortunately, this approach does not work either. What's special about the JUnit assert methods / what is SonarQube looking for specifically to check that an assertion has been made for each test?