1 files changed, 109 insertions, 0 deletions
diff --git a/DomainDigTests/DataMigrationServiceTests.swift b/DomainDigTests/DataMigrationServiceTests.swift
new file mode 100644
index 0000000..3a6cdd9
--- /dev/null
+++ b/DomainDigTests/DataMigrationServiceTests.swift
@@ -0,0 +1,109 @@
+import XCTest
+@testable import DomainDig
+
+/// Characterization tests for the versioned store-migration runner. They drive
+/// `migrateIfNeeded` against legacy on-disk fixtures in an ephemeral
+/// `UserDefaults` suite and pin the policy: forward-only, idempotent, and
+/// non-destructive to a store written by a newer build.
+///
+/// The raw storage-key strings ("trackedDomains", "watchedDomains", the legacy
+/// marker) are duplicated here on purpose — they are the on-disk contract, and
+/// hard-coding them means an accidental rename shows up as a failing migration.
+final class DataMigrationServiceTests: XCTestCase {
+    private let suiteName = "DomainDigTests.migration"
+    private var defaults: UserDefaults!
+    private let base = Date(timeIntervalSince1970: 1_700_000_000)
+
+    override func setUp() {
+        super.setUp()
+        defaults = UserDefaults(suiteName: suiteName)
+        defaults.removePersistentDomain(forName: suiteName)
+    }
+
+    override func tearDown() {
+        defaults.removePersistentDomain(forName: suiteName)
+        defaults = nil
+        super.tearDown()
+    }
+
+    func testFreshStoreIsStampedAtCurrentVersion() {
+        XCTAssertEqual(DataMigrationService.storeSchemaVersion(defaults: defaults), 0)
+
+        DataMigrationService.migrateIfNeeded(defaults: defaults)
+
+        XCTAssertEqual(
+            DataMigrationService.storeSchemaVersion(defaults: defaults),
+            DataMigrationService.currentStoreSchemaVersion
+        )
+    }
+
+    func testLegacyWatchedDomainsAreMigratedAndTheOldKeyIsDropped() throws {
+        let legacy = [WatchedDomain(domain: "legacy.example", createdAt: base, lastKnownAvailability: .registered)]
+        defaults.set(try JSONEncoder().encode(legacy), forKey: "watchedDomains")
+
+        DataMigrationService.migrateIfNeeded(defaults: defaults)
+
+        let tracked = DomainDataPortabilityService.loadTrackedDomains(defaults: defaults)
+        XCTAssertEqual(tracked.map(\.domain), ["legacy.example"])
+        XCTAssertNil(defaults.data(forKey: "watchedDomains"), "legacy key is dropped after migration")
+        XCTAssertNotNil(defaults.data(forKey: "trackedDomains"), "data is rewritten under the current key")
+        XCTAssertEqual(DataMigrationService.storeSchemaVersion(defaults: defaults), 1)
+    }
+
+    func testMigrationDeduplicatesTheStoredBlobInPlace() throws {
+        let dupes = [
+            TrackedDomain(domain: "dupe.example", updatedAt: base.addingTimeInterval(-10)),
+            TrackedDomain(domain: "DUPE.example", updatedAt: base)
+        ]
+        defaults.set(try JSONEncoder().encode(dupes), forKey: "trackedDomains")
+
+        DataMigrationService.migrateIfNeeded(defaults: defaults)
+
+        let data = try XCTUnwrap(defaults.data(forKey: "trackedDomains"))
+        let stored = try JSONDecoder().decode([TrackedDomain].self, from: data)
+        XCTAssertEqual(stored.count, 1, "the persisted blob is deduplicated, not just the load result")
+    }
+
+    func testMigrationIsIdempotent() throws {
+        defaults.set(
+            try JSONEncoder().encode([TrackedDomain(domain: "a.example", updatedAt: base)]),
+            forKey: "trackedDomains"
+        )
+
+        DataMigrationService.migrateIfNeeded(defaults: defaults)
+        let afterFirst = defaults.data(forKey: "trackedDomains")
+
+        DataMigrationService.migrateIfNeeded(defaults: defaults)
+        let afterSecond = defaults.data(forKey: "trackedDomains")
+
+        XCTAssertEqual(afterFirst, afterSecond, "a second run makes no further changes")
+        XCTAssertEqual(
+            DataMigrationService.storeSchemaVersion(defaults: defaults),
+            DataMigrationService.currentStoreSchemaVersion
+        )
+    }
+
+    func testLegacyBooleanMarkerCountsAsVersionOne() {
+        defaults.set(true, forKey: "data.migrations.v3_4_0")
+
+        XCTAssertEqual(DataMigrationService.storeSchemaVersion(defaults: defaults), 1)
+
+        // Already at v1, so the v1 step must not re-run: a leftover legacy blob
+        // is left exactly as found.
+        defaults.set(Data("x".utf8), forKey: "watchedDomains")
+        DataMigrationService.migrateIfNeeded(defaults: defaults)
+        XCTAssertNotNil(defaults.data(forKey: "watchedDomains"), "v1 is treated as already applied; no re-run")
+    }
+
+    func testNewerStoreVersionIsNeverDowngradedOrRewritten() throws {
+        let future = DataMigrationService.currentStoreSchemaVersion + 1
+        defaults.set(future, forKey: DataMigrationService.storeSchemaVersionKey)
+        let blob = try JSONEncoder().encode([TrackedDomain(domain: "keep.example", updatedAt: base)])
+        defaults.set(blob, forKey: "trackedDomains")
+
+        DataMigrationService.migrateIfNeeded(defaults: defaults)
+
+        XCTAssertEqual(DataMigrationService.storeSchemaVersion(defaults: defaults), future, "must never downgrade")
+        XCTAssertEqual(defaults.data(forKey: "trackedDomains"), blob, "future-version data is left byte-for-byte")
+    }
+}