How to compare two object with AssertJ

As an automation tester, I want to compare two objects to prove those are equal or not. To do that, I can use function of AssertJ library (assertj-core) to compare two objects field by field.

Assertion example

We have the Class User and then we create 2 objects of that class with name expectedUser and actualUser. To compare those objects, we can use following steps:

• Add assertj-core dependency to pom.xml file

<!-- https://mvnrepository.com/artifact/org.assertj/assertj-core -->
        <dependency>
            <groupId>org.assertj</groupId>
            <artifactId>assertj-core</artifactId>
            <version>3.22.0</version>
            <scope>test</scope>
        </dependency>

• The compare functions is described in following test

package info.dani.feature;

import info.dani.model.User;
import org.assertj.core.api.Assertions;
import org.junit.jupiter.api.Test;

public class WhenCompareTwoObject {
    User actualUser;
    User expectedUser;
    @Test
    public void should_be_able_to_compare_two_equal_project(){
  //Init two objects to compare
        actualUser = new User("dani",22,true,12.22);
        expectedUser = new User("dani",22,true,12.22);
  //Compare two object with AssertJ library
        Assertions.assertThat(actualUser).usingRecursiveComparison()
                .isEqualTo(expectedUser);
  //Test passed due to same value of the two objects
    }
}

That’s It! Pretty simple right!

Proven GitHub source code

The source code: here

More details about assertion example

• User class:

package info.dani.model;

public class User {
    String name;
    int age;
    Boolean isMarriage;
    double salary;

    public User(String name, int age, Boolean isMarriage, double salary) {
        this.name = name;
        this.age = age;
        this.isMarriage = isMarriage;
        this.salary = salary;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public Boolean getMarriage() {
        return isMarriage;
    }

    public void setMarriage(Boolean marriage) {
        isMarriage = marriage;
    }

    public double getSalary() {
        return salary;
    }

    public void setSalary(double salary) {
        this.salary = salary;
    }
}

• To add assertj-core dependency to pom.xml file, I am currently using version 3.22.0 to create the example, but we can use other version following our needed. With old version, we can use this function to compare two objects also:

import org.assertj.core.api.Assertions;
...
Assertions.assertThat(actualUser).isEqualToComparingFieldByField(expectedUser);
//Note: this function is deprecated in new versions of assertj-core library

• When compare two different object we can get error message that is similar to understand:

//compare
//actualUser = new User("dani",22,true,12.22);
//expectedUser = new User("Toronto23",23,false,12.22);
//Assertions.assertThat(actualUser).usingRecursiveComparison()
//                .isEqualTo(expectedUser);
//With error log:

C:\Users\admin\.jdks\corretto-11.0.14.1\bin\java.exe -ea -Didea.test.cyclic.buffer.size=1048576 "-javaagent:C:\Program Files\JetBrains\IntelliJ IDEA 2021.1\lib\idea_rt.jar=61506:C:\Program Files\JetBrains\IntelliJ IDEA 2021.1\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\JetBrains\IntelliJ IDEA 2021.1\lib\idea_rt.jar;C:\Users\admin\.m2\repository\org\junit\platform\junit-platform-launcher\1.8.2\junit-platform-launcher-1.8.2.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2021.1\plugins\junit\lib\junit5-rt.jar;C:\Program Files\JetBrains\IntelliJ IDEA 2021.1\plugins\junit\lib\junit-rt.jar;D:\OneMountWorkspace\SourceCode\BasicTecnique\target\test-classes;C:\Users\admin\.m2\repository\org\junit\jupiter\junit-jupiter\5.8.2\junit-jupiter-5.8.2.jar;C:\Users\admin\.m2\repository\org\junit\jupiter\junit-jupiter-api\5.8.2\junit-jupiter-api-5.8.2.jar;C:\Users\admin\.m2\repository\org\opentest4j\opentest4j\1.2.0\opentest4j-1.2.0.jar;C:\Users\admin\.m2\repository\org\junit\platform\junit-platform-commons\1.8.2\junit-platform-commons-1.8.2.jar;C:\Users\admin\.m2\repository\org\apiguardian\apiguardian-api\1.1.2\apiguardian-api-1.1.2.jar;C:\Users\admin\.m2\repository\org\junit\jupiter\junit-jupiter-params\5.8.2\junit-jupiter-params-5.8.2.jar;C:\Users\admin\.m2\repository\org\junit\jupiter\junit-jupiter-engine\5.8.2\junit-jupiter-engine-5.8.2.jar;C:\Users\admin\.m2\repository\org\junit\platform\junit-platform-engine\1.8.2\junit-platform-engine-1.8.2.jar;C:\Users\admin\.m2\repository\org\assertj\assertj-core\3.22.0\assertj-core-3.22.0.jar" com.intellij.rt.junit.JUnitStarter -ideVersion5 -junit5 info.dani.feature.WhenCompareTwoObject,should_be_able_to_compare_two_equal_project

java.lang.AssertionError: 
Expecting actual:
  info.dani.model.User@366647c2
to be equal to:
  info.dani.model.User@6a6afff2
when recursively comparing field by field, but found the following 3 differences:

field/property 'age' differ:
- actual value  : 22
- expected value: 23

field/property 'isMarriage' differ:
- actual value  : true
- expected value: false

field/property 'name' differ:
- actual value  : "dani"
- expected value: "Toronto23"

The recursive comparison was performed with this configuration:
- no overridden equals methods were used in the comparison (except for java types)
- these types were compared with the following comparators:
  - java.lang.Double -> DoubleComparator[precision=1.0E-15]
  - java.lang.Float -> FloatComparator[precision=1.0E-6]
  - java.nio.file.Path -> lexicographic comparator (Path natural order)
- actual and expected objects and their fields were compared field by field recursively even if they were not of the same type, this allows for example to compare a Person to a PersonDto (call strictTypeChecking(true) to change that behavior).

 at info.dani.feature.WhenCompareTwoObject.should_be_able_to_compare_two_equal_project(WhenCompareTwoObject.java:17)
 at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
... Bla Bla about some thing not so important.