refactor student and logic

src/test/java/com/ebrains/cruddemo/serviceimpl/StudentServiceImplTest.java

@@ -0,0 +1,58 @@
+package com.ebrains.cruddemo.serviceimpl;
+
+import com.ebrains.cruddemo.entity.Student;
+import com.ebrains.cruddemo.repository.StudentRepository;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.InjectMocks;
+import org.mockito.junit.jupiter.MockitoExtension;
+import java.util.Optional;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.mockito.Mockito.*;
+
+@ExtendWith(MockitoExtension.class)
+public class StudentServiceImplTest {
+
+    private final StudentRepository studentRepository = mock(StudentRepository.class);
+
+    @InjectMocks
+    private StudentServiceImpl studentService;
+
+    @Test
+    void getStudentById_found_returnsStudent() {
+        Student s = new Student();
+        when(studentRepository.findById(1L)).thenReturn(Optional.of(s));
+
+        Student result = studentService.getStudentById(1L);
+
+        assertSame(s, result);
+        verify(studentRepository).findById(1L);
+    }
+
+    @Test
+    void getStudentById_notFound_returnsNull() {
+        when(studentRepository.findById(2L)).thenReturn(Optional.empty());
+
+        Student result = studentService.getStudentById(2L);
+
+        assertNull(result);
+        verify(studentRepository).findById(2L);
+    }
+
+    @Test
+    void saveStudent_delegatesToRepository() {
+        Student s = new Student();
+
+        studentService.saveStudent(s);
+
+        verify(studentRepository).save(s);
+    }
+
+    @Test
+    void deleteStudentById_delegatesToRepository() {
+        studentService.deleteStudentById(3L);
+
+        verify(studentRepository).deleteById(3L);
+    }
+}