Write unit tests for the custom serializer

moor/test/serialization_test.dart

@@ -0,0 +1,79 @@
+import 'package:moor/moor.dart';
+import 'package:moor/src/runtime/data_class.dart';
+import 'package:test_api/test_api.dart';
+import 'data/tables/todos.dart';
+
+final someDate = DateTime(2019, 06, 08);
+
+final someTodoEntry = TodoEntry(
+  id: 3,
+  title: 'a title',
+  content: null,
+  targetDate: someDate,
+  category: 3,
+);
+
+final regularSerialized = {
+  'id': 3,
+  'title': 'a title',
+  'content': null,
+  'target_date': someDate.millisecondsSinceEpoch,
+  'category': 3,
+};
+
+final customSerialized = {
+  'id': 3,
+  'title': 'a title',
+  'content': 'set to null',
+  'target_date': someDate.toIso8601String(),
+  'category': 3,
+};
+
+class CustomSerializer extends ValueSerializer {
+  @override
+  T fromJson<T>(json) {
+    if (T == DateTime) {
+      return DateTime.parse(json.toString()) as T;
+    } else if (json == 'set to null') {
+      return null;
+    } else {
+      return json as T;
+    }
+  }
+
+  @override
+  toJson<T>(T value) {
+    if (T == DateTime) {
+      return (value as DateTime).toIso8601String();
+    } else if (value == null) {
+      return 'set to null';
+    } else {
+      return value;
+    }
+  }
+}
+
+void main() {
+  group('serialization', () {
+    test('with defaults', () {
+      expect(someTodoEntry.toJson(), equals(regularSerialized));
+    });
+
+    test('with custom serializer', () {
+      expect(someTodoEntry.toJson(serializer: CustomSerializer()),
+          equals(customSerialized));
+    });
+  });
+
+  group('deserialization', () {
+    test('with defaults', () {
+      expect(TodoEntry.fromJson(regularSerialized), equals(someTodoEntry));
+    });
+
+    test('with custom serializer', () {
+      expect(
+          TodoEntry.fromJson(customSerialized, serializer: CustomSerializer()),
+          equals(someTodoEntry));
+    });
+  });
+}