EqualsVerifier library - test hashCode() / equals() correcteness

https://www.baeldung.com/java-equals-hashcode-contracts

EqualsVerifier library.

Let's add the EqualsVerifier Maven test dependency:

<dependency>
    <groupId>nl.jqno.equalsverifier</groupId>
    <artifactId>equalsverifier</artifactId>
    <version>3.0.3</version>
    <scope>test</scope>
</dependency>
Let's verify that our Team class follows the equals() and hashCode() contracts:

@Test
public void equalsHashCodeContracts() {
    EqualsVerifier.forClass(Team.class).verify();
}
It's worth noting that EqualsVerifier tests both the equals() and hashCode() methods.

EqualsVerifier is much stricter than the Java SE contract. For example, it makes sure that our methods can't throw a NullPointerException. Also, it enforces that both methods, or the class itself, is final.

It's important to realize that the default configuration of EqualsVerifier allows only immutable fields. This is a stricter check than what the Java SE contract allows. This adheres to a recommendation of Domain-Driven Design to make value objects immutable.

If we find some of the built-in constraints unnecessary, we can add a suppress(Warning.SPECIFIC_WARNING) to our EqualsVerifier call.