test(model): add workbook, dependency and json tests

test/workbook_json_test.dart

@@ -0,0 +1,42 @@
+import 'package:cellar/cellar.dart';
+import 'package:test/test.dart';
+
+double num(CellValue value) => (value as NumberValue).value;
+
+void main() {
+  group('workbook JSON store', () {
+    test('round trips values, formulas, formats and names', () {
+      final workbook = Workbook();
+      final sheet1 = workbook.addSheet('Sheet1');
+      final data = workbook.addSheet('Data');
+      sheet1.setValue('A1', '10');
+      sheet1.setValue('A2', '20');
+      sheet1.setValue('A3', '=SUM(A1:A2)');
+      sheet1.setFormat('A3', const NumberFormat.currency('zl', before: false, thousands: false));
+      data.setValue('B1', '=Sheet1!A3 * 2');
+      workbook.defineName('Total', 'Sheet1!A3');
+
+      final encoded = encodeWorkbookJson(workbook);
+      final reloaded = decodeWorkbookJson(encoded);
+
+      expect(reloaded.sheetNames, ['Sheet1', 'Data']);
+      expect(num(reloaded.sheet('Sheet1').valueOf('A3')), 30);
+      expect(reloaded.sheet('Sheet1').displayAt(CellAddress.parse('A3')), '30.00zl');
+      expect(num(reloaded.sheet('Data').valueOf('B1')), 60);
+      expect(reloaded.resolveName('Total'), isNotNull);
+    });
+
+    test('reloaded workbook recomputes after an edit', () {
+      final workbook = Workbook();
+      final sheet1 = workbook.addSheet('Sheet1');
+      final data = workbook.addSheet('Data');
+      sheet1.setValue('A1', '5');
+      data.setValue('B1', '=Sheet1!A1 + 100');
+
+      final reloaded = decodeWorkbookJson(encodeWorkbookJson(workbook));
+      expect(num(reloaded.sheet('Data').valueOf('B1')), 105);
+      reloaded.sheet('Sheet1').setValue('A1', '7');
+      expect(num(reloaded.sheet('Data').valueOf('B1')), 107);
+    });
+  });
+}