diff --git a/lib/history/history_db.dart b/lib/history/history_db.dart
index ecf3f59..931caf4 100644
--- a/lib/history/history_db.dart
+++ b/lib/history/history_db.dart
@@ -13,6 +13,7 @@ import 'package:sqlite3/sqlite3.dart';
 /// instead, same lib, no extra layer needed.
 class HistoryDb {
   static Database? _instance;
+  static bool _useInMemory = false;
 
   static String get _stateDir => '${Platform.environment['HOME']}/.local/state/layer_wizard';
   static String get _dbPath => '$_stateDir/history.db';
@@ -25,15 +26,28 @@ class HistoryDb {
       open.overrideFor(OperatingSystem.linux, _openLinuxLibSqlite3);
     }
 
+    final db = _useInMemory ? sqlite3.openInMemory() : _openOnDisk();
+    _migrate(db);
+    _instance = db;
+    return db;
+  }
+
+  static Database _openOnDisk() {
     final dir = Directory(_stateDir);
     if (!dir.existsSync()) {
       dir.createSync(recursive: true);
     }
+    return sqlite3.open(_dbPath);
+  }
 
-    final db = sqlite3.open(_dbPath);
-    _migrate(db);
-    _instance = db;
-    return db;
+  /// Test-only: discards any open connection and makes the next
+  /// [database] call return a fresh in-memory database instead of touching
+  /// the real `~/.local/state/layer_wizard/history.db`. Call this from
+  /// `setUp` in every test that exercises [HistoryService].
+  static void resetForTesting() {
+    _instance?.dispose();
+    _instance = null;
+    _useInMemory = true;
   }
 
   static DynamicLibrary _openLinuxLibSqlite3() {
diff --git a/lib/history/history_service.dart b/lib/history/history_service.dart
index aa658a8..80552c5 100644
--- a/lib/history/history_service.dart
+++ b/lib/history/history_service.dart
@@ -27,12 +27,15 @@ class HistoryService {
   /// Compares the live `rpm-ostree status` against our DB and brings
   /// `current` (and, on first run, `last_known_safe`) up to date. Safe to
   /// call on every launch — a no-op if nothing has changed since last time.
-  Future<LayerNode> reconcile() async {
+  ///
+  /// [deployments] overrides the live query — tests pass a fixed list so
+  /// they don't depend on `rpm-ostree` actually being present/accurate.
+  Future<LayerNode> reconcile({List<DeploymentInfo>? deployments}) async {
     final db = _db;
-    final deployments = await OstreeService.getAllDeployments();
-    final booted = deployments.firstWhere(
+    final deps = deployments ?? await OstreeService.getAllDeployments();
+    final booted = deps.firstWhere(
       (d) => d.booted,
-      orElse: () => deployments.first,
+      orElse: () => deps.first,
     );
 
     LayerNode node;
diff --git a/test/history_service_test.dart b/test/history_service_test.dart
new file mode 100644
index 0000000..4f11d61
--- /dev/null
+++ b/test/history_service_test.dart
@@ -0,0 +1,128 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:layer_wizard/history/history_db.dart';
+import 'package:layer_wizard/history/history_service.dart';
+import 'package:layer_wizard/ostree_service.dart';
+
+DeploymentInfo _deployment({
+  required String checksum,
+  bool booted = false,
+  bool staged = false,
+  String version = 'v1',
+  List<String> requestedPackages = const [],
+}) {
+  return DeploymentInfo(
+    version: version,
+    checksum: checksum,
+    containerImageRef: 'ostree-image-signed:docker://ghcr.io/ublue-os/aurora:stable',
+    requestedPackages: requestedPackages,
+    booted: booted,
+    staged: staged,
+  );
+}
+
+void main() {
+  final history = HistoryService.instance;
+
+  setUp(() {
+    HistoryDb.resetForTesting();
+  });
+
+  test('first reconcile bootstraps a root node and both pointers', () async {
+    final a = _deployment(checksum: 'aaa', booted: true);
+
+    final current = await history.reconcile(deployments: [a]);
+
+    expect(current.checksum, 'aaa');
+    expect(current.parentId, isNull);
+    expect(current.source, 'detected');
+
+    final safe = await history.getLastKnownSafe();
+    expect(safe?.checksum, 'aaa');
+  });
+
+  test('reconcile is idempotent for an already-known checksum', () async {
+    final a = _deployment(checksum: 'aaa', booted: true);
+    await history.reconcile(deployments: [a]);
+
+    await history.reconcile(deployments: [a]);
+    await history.reconcile(deployments: [a]);
+
+    final all = await history.getAllNodes();
+    expect(all, hasLength(1));
+  });
+
+  test('recordInstall adds a child of current without moving current', () async {
+    final a = _deployment(checksum: 'aaa', booted: true);
+    final root = await history.reconcile(deployments: [a]);
+
+    final staged = _deployment(checksum: 'bbb', staged: true, requestedPackages: ['vim']);
+    final node = await history.recordInstall(packageName: 'vim', staged: staged);
+
+    expect(node.parentId, root.id);
+    expect(node.action, 'install');
+    expect(node.source, 'layer_wizard');
+    expect(node.packageName, 'vim');
+
+    final current = await history.getCurrent();
+    expect(current?.id, root.id, reason: 'current must not move until the staged deployment is booted');
+  });
+
+  test('rebooting into a staged install moves current without a duplicate row', () async {
+    final a = _deployment(checksum: 'aaa', booted: true);
+    await history.reconcile(deployments: [a]);
+
+    final staged = _deployment(checksum: 'bbb', staged: true, requestedPackages: ['vim']);
+    final installed = await history.recordInstall(packageName: 'vim', staged: staged);
+
+    final bootedAfterReboot = _deployment(checksum: 'bbb', booted: true, requestedPackages: ['vim']);
+    final current = await history.reconcile(deployments: [bootedAfterReboot]);
+
+    expect(current.id, installed.id);
+    final all = await history.getAllNodes();
+    expect(all, hasLength(2), reason: 'no new row — same checksum as the staged install');
+  });
+
+  test('a manual change (unknown checksum) is recorded as detected, parented on current', () async {
+    final a = _deployment(checksum: 'aaa', booted: true);
+    final root = await history.reconcile(deployments: [a]);
+
+    final manual = _deployment(checksum: 'ccc', booted: true, requestedPackages: ['htop']);
+    final current = await history.reconcile(deployments: [manual]);
+
+    expect(current.checksum, 'ccc');
+    expect(current.source, 'detected');
+    expect(current.parentId, root.id);
+
+    final all = await history.getAllNodes();
+    expect(all, hasLength(2));
+  });
+
+  test('markCurrentAsSafe moves last_known_safe to the current node', () async {
+    final a = _deployment(checksum: 'aaa', booted: true);
+    await history.reconcile(deployments: [a]);
+
+    final b = _deployment(checksum: 'bbb', booted: true);
+    await history.reconcile(deployments: [b]);
+
+    expect((await history.getLastKnownSafe())?.checksum, 'aaa');
+
+    await history.markCurrentAsSafe();
+
+    expect((await history.getLastKnownSafe())?.checksum, 'bbb');
+  });
+
+  test('getChainToCurrent walks root to current in order', () async {
+    final a = _deployment(checksum: 'aaa', booted: true);
+    await history.reconcile(deployments: [a]);
+
+    final staged = _deployment(checksum: 'bbb', staged: true, requestedPackages: ['vim']);
+    await history.recordInstall(packageName: 'vim', staged: staged);
+
+    final bootedAfterReboot = _deployment(checksum: 'bbb', booted: true, requestedPackages: ['vim']);
+    await history.reconcile(deployments: [bootedAfterReboot]);
+
+    final chain = await history.getChainToCurrent();
+
+    expect(chain.map((n) => n.checksum), ['aaa', 'bbb']);
+  });
+}
diff --git a/test/widget_test.dart b/test/widget_test.dart
index 28e96b3..6acc480 100644
--- a/test/widget_test.dart
+++ b/test/widget_test.dart
@@ -5,12 +5,17 @@ import 'package:layer_wizard/main.dart';
 
 void main() {
   testWidgets('app boots without crashing', (WidgetTester tester) async {
-    await tester.pumpWidget(const LayerWizardApp());
-    // Intentionally a single pump, not pumpAndSettle: startup kicks off real
-    // async work (reading a file, running `rpm-ostree status`) behind a
-    // CircularProgressIndicator, which never "settles". This just checks
-    // the app renders its initial loading frame without throwing.
-    await tester.pump();
+    // Startup kicks off real async work (reading a file, running
+    // `rpm-ostree status`, opening the history DB) behind a
+    // CircularProgressIndicator that never "settles" within this test, so
+    // this only checks the initial loading frame renders without throwing.
+    // runAsync is required because that startup work includes real
+    // dart:io Process/FFI calls — without it, flutter_test's fake-time zone
+    // flags a dangling Timer from the real I/O once the tree is disposed.
+    await tester.runAsync(() async {
+      await tester.pumpWidget(const LayerWizardApp());
+      await tester.pump();
+    });
 
     expect(find.byType(CircularProgressIndicator), findsOneWidget);
   });