add TorchState test

+import 'package:flutter_test/flutter_test.dart';
+import 'package:mobile_scanner/src/enums/torch_state.dart';
+
+void main() {
+  group('$TorchState tests', () {
+    test('can be created from raw value', () {
+      const values = <int, TorchState>{
+        0: TorchState.off,
+        1: TorchState.on,
+      };
+
+      for (final MapEntry<int, TorchState> entry in values.entries) {
+        final TorchState result = TorchState.fromRawValue(entry.key);
+
+        expect(result, entry.value);
+      }
+    });
+
+    test('invalid raw value throws argument error', () {
+      const int negative = -1;
+      const int outOfRange = 2;
+
+      expect(() => TorchState.fromRawValue(negative), throwsArgumentError);
+      expect(() => TorchState.fromRawValue(outOfRange), throwsArgumentError);
+    });
+
+    test('can be converted to raw value', () {
+      const values = <TorchState, int>{
+        TorchState.off: 0,
+        TorchState.on: 1,
+      };
+
+      for (final MapEntry<TorchState, int> entry in values.entries) {
+        final int result = entry.key.rawValue;
+
+        expect(result, entry.value);
+      }
+    });
+  });
+}