How do I negate assertions in AssertJ?

Question

Using Hamcrest it is easily possible to negate a matcher. E.g. you can write an assertion like this:

assertThat("The dog bites Tom", not(stringContainsInOrder(Arrays.asList("Tom", "dog"))));

I.e. using the org.hamcrest.core.IsNot , org.hamcrest.core.AnyOf matchers it is easy to combine or negate assertions.

Is there any equivalent in AssertJ? I know that it is possible to combine/negate Conditions. But what about normal assertion methods? E.g. what do you do if you want to test that a String does not consists only of digits, i.e. negate the following assertion:

assertThat("1234xxx5678").containsOnlyDigits();

Answer 1

It is not possible to combine normal assertions methods, this is an area where Hamcrest is more flexible than AssertJ.

In your case I would write a Condition as you suggested or use a lambda with matches assertion.

Answer 2

This will do the trick:

assertThat(Collections.singleton("1234xxx5678")).noneSatisfy(candidate -> 
    assertThat(candidate).containsOnlyDigits()
);

Slightly hacky, and the clarity of intention is not quite up to normal assertJ standards, but for the completely general case of negating any assertion it is what we have so far.

A fluent not() would be confusing when combined with chained asserts, but I do wish we could have a general doesNotSatisfy(Consumer) on AbstractObjectAssert