Update internals of ProblemImpl

Author: malczuuu

src/main/java/io/github/malczuuu/problem4j/core/ProblemImpl.java

@@ -10,7 +10,7 @@
 import java.util.Set;
 import java.util.stream.Collectors;
 
-class ProblemImpl implements Problem {
+final class ProblemImpl implements Problem {
 
   private static final long serialVersionUID = 1L;
 
@@ -94,11 +94,14 @@ public boolean hasExtension(String extension) {
   }
 
   @Override
-  public boolean equals(Object o) {
-    if (!(o instanceof ProblemImpl)) {
+  public boolean equals(Object obj) {
+    if (this == obj) {
+      return true;
+    }
+    if (obj == null || getClass() != obj.getClass()) {
       return false;
     }
-    ProblemImpl problem = (ProblemImpl) o;
+    ProblemImpl problem = (ProblemImpl) obj;
     return Objects.equals(getType(), problem.getType())
         && Objects.equals(getTitle(), problem.getTitle())
         && getStatus() == problem.getStatus()
@@ -187,6 +190,9 @@ public Object setValue(Object value) {
 
     @Override
     public boolean equals(Object obj) {
+      if (this == obj) {
+        return true;
+      }
       if (obj == null || getClass() != obj.getClass()) {
         return false;
       }

src/test/java/io/github/malczuuu/problem4j/core/ProblemExceptionTests.java

@@ -2,6 +2,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
 
 import org.junit.jupiter.api.Test;
 
@@ -144,4 +145,53 @@ void givenProblemWithSpecialCharacters_whenCreatingException_thenSpecialCharacte
         "Validation Error: Required Fields Missing: Fields 'name' & 'email' are required (check docs) (code: 422)",
         exception.getMessage());
   }
+
+  @Test
+  void givenCtor_whenCreatingProblemException_problemIsNotRecreated() {
+    Problem problem = Problem.builder().title("Bad Request").status(400).build();
+
+    ProblemException exception = new ProblemException(problem);
+
+    assertSame(problem, exception.getProblem());
+  }
+
+  @Test
+  void givenCtorWithMessage_whenCreatingProblemException_problemIsNotRecreated() {
+    Problem problem = Problem.builder().title("Bad Request").status(400).build();
+
+    ProblemException exception = new ProblemException("this is a message", problem);
+
+    assertSame(problem, exception.getProblem());
+  }
+
+  @Test
+  void givenCtorWithCause_whenCreatingProblemException_problemIsNotRecreated() {
+    Problem problem = Problem.builder().title("Bad Request").status(400).build();
+    Throwable cause = new RuntimeException("root cause");
+
+    ProblemException exception = new ProblemException(problem, cause);
+
+    assertSame(problem, exception.getProblem());
+  }
+
+  @Test
+  void givenCtorWithMessageAndCause_whenCreatingProblemException_problemIsNotRecreated() {
+    Problem problem = Problem.builder().title("Bad Request").status(400).build();
+    Throwable cause = new RuntimeException("root cause");
+
+    ProblemException exception = new ProblemException("this is a message", problem, cause);
+
+    assertSame(problem, exception.getProblem());
+  }
+
+  @Test
+  void givenCtorWithParameters_whenCreatingProblemException_problemIsNotRecreated() {
+    Problem problem = Problem.builder().title("Bad Request").status(400).build();
+    Throwable cause = new RuntimeException("root cause");
+
+    ProblemException exception =
+        new ProblemException("this is a message", problem, cause, false, true);
+
+    assertSame(problem, exception.getProblem());
+  }
 }