Add unit tests for subscriber service

src/test/java/de/bund/digitalservice/a2j/service/subscriber/FitConnectSubscriberServiceTest.java

@@ -0,0 +1,42 @@
+package de.bund.digitalservice.a2j.service.subscriber;
+
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+import dev.fitko.fitconnect.api.domain.model.submission.SubmissionForPickup;
+import dev.fitko.fitconnect.api.domain.subscriber.ReceivedSubmission;
+import dev.fitko.fitconnect.client.SubscriberClient;
+import java.util.List;
+import java.util.UUID;
+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.springframework.boot.test.mock.mockito.MockBean;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+@ExtendWith(SpringExtension.class)
+class FitConnectSubscriberServiceTest {
+  private SubscriberService service;
+
+  @MockBean SubscriberClient client;
+
+  @Mock ReceivedSubmission receivedSubmission;
+  @Mock SubmissionForPickup submissionForPickup;
+
+  @BeforeEach
+  void setup() {
+    this.service = new FitConnectSubscriberService(client);
+  }
+
+  @Test
+  void testPickUpSubmission() {
+    when(client.requestSubmission(submissionForPickup)).thenReturn(receivedSubmission);
+    when(receivedSubmission.getSubmissionId()).thenReturn(UUID.randomUUID());
+
+    service.pickUpSubmission(submissionForPickup);
+
+    verify(client).requestSubmission(submissionForPickup);
+    verify(receivedSubmission).acceptSubmission();
+  }
+}