Better reporting on usingRecursiveFieldByFieldElementComparator() for list of objects

[harishkannarao]

Summary

Provide better reporting on differences (Path to difference:) along with object's toString() during assertion failure when comparing lists of objects

Example

@Test
    public void sampleTest() throws Exception {
        List<MyClass> myClasses = Arrays.asList(
                new MyClass("type1", new MySubClass("sub_type1")),
                new MyClass("type2", new MySubClass("sub_type2"))
        );

        assertThat(myClasses)
                .usingRecursiveFieldByFieldElementComparator()
                .containsExactly(
                        new MyClass("type1", new MySubClass("sub_type1")),
                        new MyClass("type2", new MySubClass("sub_type3"))
                );

    }

    public static class MyClass {
        private final String type;
        private final MySubClass mySubClass;

        public MyClass(String type, MySubClass mySubClass) {
            this.type = type;
            this.mySubClass = mySubClass;
        }
    }

    public static class MySubClass {
        private final String type;

        public MySubClass(String type) {
            this.type = type;
        }
    }

[joel-costigliola]

What outcome would like to see ?

[harishkannarao]

I have enhanced the sample test. On failure, the second test gives additional information Path to difference: as which helps to quickly identify the elements that differ between lists.

Path to difference:  <mySubClass.type>
- expected: <sub_type3>
- actual  : <sub_type2>

package com.harishkannarao;

import org.junit.Test;

import java.util.Arrays;
import java.util.List;

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

public class SampleListComparisonTest {

    @Test
    public void listComparisonConventional() throws Exception {
        List<MyClass> myClasses = Arrays.asList(
                new MyClass("type1", new MySubClass("sub_type1")),
                new MyClass("type2", new MySubClass("sub_type2"))
        );

        assertThat(myClasses)
                .usingRecursiveFieldByFieldElementComparator()
                .containsExactly(
                        new MyClass("type1", new MySubClass("sub_type1")),
                        new MyClass("type2", new MySubClass("sub_type3"))
                );

    }

    @Test
    public void listComparisonHackyWay() throws Exception {
        List<MyClass> myClassesActual = Arrays.asList(
                new MyClass("type1", new MySubClass("sub_type1")),
                new MyClass("type2", new MySubClass("sub_type2"))
        );

        List<MyClass> myClassesExpected = Arrays.asList(
                new MyClass("type1", new MySubClass("sub_type1")),
                new MyClass("type2", new MySubClass("sub_type3"))
        );


        assertThat((Object) myClassesActual.toArray())
                .isEqualToComparingFieldByFieldRecursively(
                        myClassesExpected.toArray()
                );

    }

    public static class MyClass {
        private final String type;
        private final MySubClass mySubClass;

        public MyClass(String type, MySubClass mySubClass) {
            this.type = type;
            this.mySubClass = mySubClass;
        }
    }

    public static class MySubClass {
        private final String type;

        public MySubClass(String type) {
            this.type = type;
        }
    }
}

[jomora]

I have to compare very deep structures of objects with many attributes. This is quite tedious and I'm really looking forward to be able to use this feature! :-) Thx in advance!

[joel-costigliola]

I agree with the issue raised, it turns out it is not as simple to fix with the current design, I'm gonna add this as another requirement for #1002 (New recursive comparison api).

In the meantime the best way to have detailed error is to cast the collection to Object and use isEqualToComparingFieldByFieldRecursively as suggested by @harishkannarao:

assertThat((Object) myClassesActual)
                .isEqualToComparingFieldByFieldRecursively(myClassesExpected);

Note that you don't have to convert collections to arrays for this to work.

[joel-costigliola]

I'm closing this issue as it is going to be addressed in #1002.