Add unit tests for exam scoring service

src/test/java/com/example/questionbank/service/quiz/ExamScoringServiceTest.java

@@ -0,0 +1,37 @@
+package com.example.questionbank.service.quiz;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import com.example.questionbank.domain.enumeration.OptionKey;
+import org.junit.jupiter.api.Test;
+
+class ExamScoringServiceTest {
+
+    private final ExamScoringService service = new ExamScoringService();
+
+    @Test
+    void correctAnswerGetsOnePoint() {
+        var result = service.score(OptionKey.A, OptionKey.A);
+
+        assertTrue(result.correct());
+        assertEquals(1, result.awardedPoints());
+    }
+
+    @Test
+    void wrongAnswerGetsZeroPoints() {
+        var result = service.score(OptionKey.A, OptionKey.D);
+
+        assertFalse(result.correct());
+        assertEquals(0, result.awardedPoints());
+    }
+
+    @Test
+    void unansweredQuestionGetsZeroPoints() {
+        var result = service.score(OptionKey.A, null);
+
+        assertFalse(result.correct());
+        assertEquals(0, result.awardedPoints());
+    }
+}