added some basic tests

obs/obs-service-impl/src/test/java/com/adorsys/webank/obs/serviceimpl/RegistrationServiceImplTest.java

@@ -0,0 +1,21 @@
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import org.junit.jupiter.api.Test;
+import com.adorsys.webank.obs.serviceimpl.RegistrationServiceImpl;
+
+public class RegistrationServiceImplTest {
+
+    private final RegistrationServiceImpl registrationService = new RegistrationServiceImpl();
+
+    @Test
+    public void testRegisterAccountSuccess() {
+        // Arrange
+        String phoneNumber = "1234567890";
+        String publicKey = "dummyPublicKey";
+
+        // Act
+        String result = registrationService.registerAccount(phoneNumber, publicKey);
+
+        // Assert
+        assertEquals("Successfully registered account for phone number: 1234567890", result);
+    }
+}