How can I assert that all elements in a collection meet a specific condition using AssertJ?

General Discussions
1

I’m using AssertJ and need to verify that every object in a list satisfies a certain condition for example, ensuring all objects have intField > 0. My current attempt looks like this:

assertThat(myObjectList).extracting(p -> p.getIntField()).isGreaterThan(0);

However, this doesn’t seem to work as expected. What’s the right way to assert that all elements in a collection meet the same condition? Should I use allSatisfy() or a different AssertJ approach?

2

AssertJ provides the allSatisfy method to assert a condition on every element individually:

import static org.assertj.core.api.Assertions.assertThat;

assertThat(myObjectList).allSatisfy(obj -> 
    assertThat(obj.getIntField()).isGreaterThan(0)
);

This runs the lambda for each element, and the assertion fails if any element doesn’t meet the condition. It’s very readable and keeps the logic close to the element.

3

If you prefer a more functional style, you can extract the field and use allMatch with a predicate:

assertThat(myObjectList)
    .extracting(MyObject::getIntField)
    .allMatch(value -> (Integer) value > 0);

This way, you assert that all extracted values satisfy your predicate. Remember to cast properly since extracting() can return Object unless you use extractingInt.

4

For numeric fields, extractingInt is convenient and avoids boxing:

assertThat(myObjectList)
    .extractingInt(MyObject::getIntField)
    .allMatch(i -> i > 0);

This approach is concise and efficient because it deals directly with primitives and works well for fields like int or long.