usingRecursiveComparison() not working when Class implements Iterable

Summary

When asserting 2 objects are equal usingRecursiveComparison(), when the class implements Iterable, seems to cause an equals check only the iterable objects, and not the parent object. Noticed this in a more complicated Class, so mocked up an example.

In the below example, the assert in the test passes, even when the objects aren’t equal. Having followed through the code during debug, it seems if the class implements Iterable, the checks for all other variables are not performed. Tested using assertj version 3.23.1.

Example

import org.junit.jupiter.api.Test;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

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

public class SomeTest {
  public static class SomeEntry {
    private String a;

    public SomeEntry(String a) {
      this.a = a;
    }
  }

  public static class SomeIterable implements Iterable<SomeEntry>{
    private final List<SomeEntry> entries = new ArrayList<>();
    private final String name;

    public SomeIterable(String name) {
      this.name = name;
    }

    @Override
    public Iterator<SomeEntry> iterator() {
      return entries.iterator();
    }
  }


  @Test
  public void test() {
    assertThat(new SomeIterable("bob")).usingRecursiveComparison().isEqualTo(new SomeIterable("dave"));
  }
}

[linksblackmask]

Sorry wasn’t really thinking this morning when I woke up - yes you’re right, simply checking for instanceOf Collection won’t work. Got to say this has been a proper head scratcher.

Thinking from the perspective of what should recursiveComparison mean; I think the default behaviour, especially when equality checking, is recursively assessing all feilds are equal.

A possible solution would be to have the iterables fields from the JDK be ignored by default; and for everything else, check them, and obviously throw errors if they don’t match, adding methods like:

.ignoreAllFieldsFromIterable(Class clazz) .ignoreAllFieldsFromIterableClassesIn(String package) > .ignoreFieldsFromIterable(Class clazz, String… fields)

Then as an error message give a solution. So something like "field x in class y doesn’t match expected, should this be asserted? Use method <methodName> to ignore this field or <methodName> to ignore all fields asides from the iterator in class <clazz>.

What do you think @joel-costigliola ?

Edit - The bottom method would be covered by the ignore ignoreFields() method already.

[joel-costigliola]

Checking only iterable and collection would not work if you had extended List so I feel checking if the iterable belongs to the JDK is better (but that would not cover the case where the iterable comes from a lib like Guava), I don’t think we can find a perfect check here (maybe I’m wrong).