tests: add recovery mnemonic tests

test/slip39_test.dart

@@ -0,0 +1,66 @@
+import 'dart:typed_data';
+
+import 'package:convert/convert.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:slip39/slip39.dart';
+
+void main() {
+  testWidgets('Test 2/5 without passphrase', (WidgetTester tester) async {
+    var scheme = [
+      for (var i = 0; i < 5; i++) [1, 1]
+    ];
+    const inputSecret =
+        'fd43b5abd947c9a8c55416008840537ab40bde5ab6d315fbcad5938302f78ec6';
+    const threshold = 2;
+
+    final created = Slip39.from(
+      scheme,
+      masterSecret: Uint8List.fromList(hex.decode(inputSecret)),
+      passphrase: '',
+      threshold: threshold,
+    );
+
+    List<String> shares = [];
+    for (var i = 0; i < created.groupCount; i++) {
+      shares.addAll(created.fromPath('r/$i').mnemonics);
+    }
+
+    List<int> recovered = Slip39.recoverSecret(
+      [shares[0], shares[1]],
+      passphrase: '',
+    );
+
+    final outputSecret = hex.encode(recovered);
+    expect(inputSecret, outputSecret);
+  });
+
+  testWidgets('Test 3/5 without passphrase', (WidgetTester tester) async {
+    var scheme = [
+      for (var i = 0; i < 5; i++) [1, 1]
+    ];
+    const inputSecret =
+        '99e0cda36055002ea4c60fcdbbe1d76beff3e7bcb421ab0db0fa1e034385f5c3';
+    const passphrase = 'azerty';
+    const threshold = 3;
+
+    final created = Slip39.from(
+      scheme,
+      masterSecret: Uint8List.fromList(hex.decode(inputSecret)),
+      passphrase: passphrase,
+      threshold: threshold,
+    );
+
+    List<String> shares = [];
+    for (var i = 0; i < created.groupCount; i++) {
+      shares.addAll(created.fromPath('r/$i').mnemonics);
+    }
+
+    final recovered = Slip39.recoverSecret(
+      [shares[0], shares[1], shares[4]],
+      passphrase: passphrase,
+    );
+
+    final outputSecret = hex.encode(recovered);
+    expect(inputSecret, outputSecret);
+  });
+}