added ConnectionService and HomeboxProvider tests

backend/src/test/java/com/vaessl/app/connection/ConnectionServiceTest.java

@@ -0,0 +1,50 @@
+package com.vaessl.app.connection;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.doThrow;
+import static org.mockito.Mockito.never;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import java.util.List;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import com.vaessl.app.dto.ConnectionRequest;
+import com.vaessl.app.exception.EmptyCredentialsException;
+
+import static com.vaessl.app.connection.Mockdata.*;
+
+@ExtendWith(MockitoExtension.class)
+class ConnectionServiceTest {
+
+    @Mock
+    private ConnectionProvider mockProvider;
+    @Mock
+    private ConnectionRepository mockRepo;
+
+    private ConnectionService connectionService;
+
+    @BeforeEach
+    void setup() {
+        when(mockProvider.getServiceType()).thenReturn(MOCK_SERVICE_TYPE);
+        connectionService = new ConnectionService(List.of(mockProvider), mockRepo);
+    }
+
+    @Test
+    void login_ShouldAbort_WhenCheckCredentialsThrowsException() {
+        ConnectionRequest request = new ConnectionRequest(MOCK_URL, MOCK_SERVICE_TYPE, null, null, false);
+
+        doThrow(new EmptyCredentialsException(List.of("username")))
+            .when(mockProvider).checkCredentials(request);
+
+        assertThrows(EmptyCredentialsException.class, () -> connectionService.login(request));
+
+        verify(mockProvider, never()).authenticate(any());
+    }
+}