Use EqualsVerifier to ensure that equals has been implemented correctly

pom.xml

@@ -5,7 +5,7 @@
   <modelVersion>4.0.0</modelVersion>
   <groupId>edu.hm.hafner</groupId>
   <artifactId>codingstyle</artifactId>
-  <version>2.1.1-SNAPSHOT</version>
+  <version>2.2.0-SNAPSHOT</version>
 
   <packaging>jar</packaging>
 
@@ -62,6 +62,7 @@
     <javax.annotation-api.version>1.3.2</javax.annotation-api.version>
 
     <!-- Project Test Dependencies Configuration -->
+    <equalsverifier.version>3.5.5</equalsverifier.version>
     <junit.version>5.7.1</junit.version>
     <junit-platform-launcher.version>1.7.1</junit-platform-launcher.version>
     <mockito.version>3.8.0</mockito.version>
@@ -103,7 +104,6 @@
 
     <!-- Maven Surefire ArgLine -->
     <argLine>-Djava.util.logging.config.file=logging.properties</argLine>
-
   </properties>
 
   <dependencyManagement>
@@ -144,6 +144,12 @@
     </dependency>
 
     <!-- Test Dependencies -->
+    <dependency>
+      <groupId>nl.jqno.equalsverifier</groupId>
+      <artifactId>equalsverifier</artifactId>
+      <version>${equalsverifier.version}</version>
+      <scope>test</scope>
+    </dependency>
     <dependency>
       <groupId>org.junit.jupiter</groupId>
       <artifactId>junit-jupiter-api</artifactId>

src/test/java/edu/hm/hafner/util/FilteredLogTest.java

@@ -2,6 +2,8 @@
 
 import org.junit.jupiter.api.Test;
 
+import nl.jqno.equalsverifier.EqualsVerifier;
+
 import static edu.hm.hafner.util.assertions.Assertions.*;
 
 /**
@@ -125,4 +127,9 @@ void shouldManuallyUseSerializationHelpers() {
 
         assertThat(restored).isEqualTo(serializable);
     }
+
+    @Test
+    void shouldObeyEqualsContract() {
+        EqualsVerifier.simple().forClass(FilteredLog.class).verify();
+    }
 }

src/test/java/edu/hm/hafner/util/TreeStringBuilderTest.java

@@ -7,6 +7,8 @@
 
 import org.junit.jupiter.api.Test;
 
+import nl.jqno.equalsverifier.EqualsVerifier;
+
 import static org.assertj.core.api.Assertions.*;
 
 /**
@@ -115,4 +117,12 @@ void shouldCreateRandomTreeStrings() {
             assertThat(o.get(i)).hasToString(a.get(i));
         }
     }
+
+    @Test
+    void shouldObeyEqualsContract() {
+        EqualsVerifier.simple()
+                .withPrefabValues(TreeString.class, TreeString.valueOf("One"), TreeString.valueOf("Teo"))
+                .forClass(TreeString.class)
+                .verify();
+    }
 }