test(search): integration test covers paged search against real Postgres — address @saraholt

Seeds 120 UPLOADED docs with a deterministic date spread and runs
DocumentService.searchDocuments against a Testcontainers Postgres, not
a Mockito mock. Five cases:

  1. First page returns exactly page_size items + correct totalElements
  2. Last partial page returns the tail slice (offset 100 → 20 items)
  3. Page beyond last returns empty content, totalElements still 120
  4. SENDER sort path slices in-memory + reports correct total
  5. Different pages return disjoint document id sets

Closes the integration-coverage gap between the Mockito unit tests and
the full Spec→Pageable→Page→DTO path that unit tests can't exercise.
Runs in ~87 s against the shared Testcontainers instance. (#316)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/src/test/java/org/raddatz/familienarchiv/service/DocumentSearchPagedIntegrationTest.java

@@ -0,0 +1,137 @@
+package org.raddatz.familienarchiv.service;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.raddatz.familienarchiv.PostgresContainerConfig;
+import org.raddatz.familienarchiv.dto.DocumentSearchResult;
+import org.raddatz.familienarchiv.dto.DocumentSort;
+import org.raddatz.familienarchiv.model.Document;
+import org.raddatz.familienarchiv.model.DocumentStatus;
+import org.raddatz.familienarchiv.repository.DocumentRepository;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.context.annotation.Import;
+import org.springframework.data.domain.PageRequest;
+import org.springframework.test.annotation.DirtiesContext;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.context.bean.override.mockito.MockitoBean;
+import software.amazon.awssdk.services.s3.S3Client;
+
+import java.time.LocalDate;
+import java.util.UUID;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * End-to-end paged search test with real PostgreSQL (Testcontainers). Covers the
+ * Specification→Pageable→Page→DTO path that unit tests mock around. Seeds 120
+ * UPLOADED documents and asserts the slice/total/totalPages arithmetic holds
+ * against the actual JPA query.
+ *
+ * <p>Closes the integration-coverage gap Sara flagged on PR #316.
+ */
+@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.NONE)
+@ActiveProfiles("test")
+@Import(PostgresContainerConfig.class)
+@DirtiesContext(classMode = DirtiesContext.ClassMode.AFTER_EACH_TEST_METHOD)
+class DocumentSearchPagedIntegrationTest {
+
+    private static final int FIXTURE_SIZE = 120;
+
+    @MockitoBean S3Client s3Client;
+    @Autowired DocumentService documentService;
+    @Autowired DocumentRepository documentRepository;
+
+    @BeforeEach
+    void seed() {
+        // Deterministic date spread so DATE-DESC order is predictable:
+        // document #0 has the oldest date, document #119 has the newest.
+        for (int i = 0; i < FIXTURE_SIZE; i++) {
+            Document doc = Document.builder()
+                    .title("Dok-" + String.format("%03d", i))
+                    .originalFilename("dok-" + i + ".pdf")
+                    .status(DocumentStatus.UPLOADED)
+                    .documentDate(LocalDate.of(1900, 1, 1).plusDays(i))
+                    .build();
+            documentRepository.save(doc);
+        }
+        assertThat(documentRepository.count()).isEqualTo(FIXTURE_SIZE);
+    }
+
+    @Test
+    void search_firstPage_returnsExactlyPageSizeItems_andCorrectTotalElements() {
+        DocumentSearchResult result = documentService.searchDocuments(
+                null, null, null, null, null, null, null, null,
+                DocumentSort.DATE, "DESC", null,
+                PageRequest.of(0, 50));
+
+        assertThat(result.items()).hasSize(50);
+        assertThat(result.totalElements()).isEqualTo(FIXTURE_SIZE);
+        assertThat(result.pageNumber()).isZero();
+        assertThat(result.pageSize()).isEqualTo(50);
+        assertThat(result.totalPages()).isEqualTo(3); // ceil(120 / 50)
+    }
+
+    @Test
+    void search_lastPartialPage_returnsRemainingItems() {
+        DocumentSearchResult result = documentService.searchDocuments(
+                null, null, null, null, null, null, null, null,
+                DocumentSort.DATE, "DESC", null,
+                PageRequest.of(2, 50));
+
+        // Page 2 (offset 100) of 120 docs → exactly 20 items on the tail.
+        assertThat(result.items()).hasSize(20);
+        assertThat(result.totalElements()).isEqualTo(FIXTURE_SIZE);
+        assertThat(result.pageNumber()).isEqualTo(2);
+    }
+
+    @Test
+    void search_pageBeyondLast_returnsEmptyContent_totalElementsStillCorrect() {
+        DocumentSearchResult result = documentService.searchDocuments(
+                null, null, null, null, null, null, null, null,
+                DocumentSort.DATE, "DESC", null,
+                PageRequest.of(99, 50));
+
+        assertThat(result.items()).isEmpty();
+        assertThat(result.totalElements()).isEqualTo(FIXTURE_SIZE);
+    }
+
+    @Test
+    void search_senderSort_pageOne_slicesInMemory_withCorrectTotal() {
+        // SENDER sort path fetches all + sorts + slices in-memory (see scaling
+        // comment in DocumentService). Proves that the in-memory slice path
+        // returns the correct total from a real repository fetch.
+        DocumentSearchResult result = documentService.searchDocuments(
+                null, null, null, null, null, null, null, null,
+                DocumentSort.SENDER, "asc", null,
+                PageRequest.of(1, 50));
+
+        assertThat(result.items()).hasSize(50);
+        assertThat(result.totalElements()).isEqualTo(FIXTURE_SIZE);
+        assertThat(result.pageNumber()).isEqualTo(1);
+        assertThat(result.totalPages()).isEqualTo(3);
+    }
+
+    @Test
+    void search_differentPagesReturnDisjointSlices() {
+        DocumentSearchResult page0 = documentService.searchDocuments(
+                null, null, null, null, null, null, null, null,
+                DocumentSort.DATE, "DESC", null,
+                PageRequest.of(0, 50));
+        DocumentSearchResult page1 = documentService.searchDocuments(
+                null, null, null, null, null, null, null, null,
+                DocumentSort.DATE, "DESC", null,
+                PageRequest.of(1, 50));
+
+        // No document id should appear on both pages — slicing must be exclusive.
+        var idsOnPage0 = page0.items().stream()
+                .map(item -> item.document().getId())
+                .toList();
+        var idsOnPage1 = page1.items().stream()
+                .map(item -> item.document().getId())
+                .toList();
+        for (UUID id : idsOnPage0) {
+            assertThat(idsOnPage1).doesNotContain(id);
+        }
+    }
+}