Define a new data model that uses data from the cognitive_data

lib/src/digit_span_task/components/data/digit_span_task_data.dart

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+import 'package:cognitive_data/cognitive_data.dart';
+
+/// Structured data collected for a single session.
+/// Includes data about the [trials] (practice and experimental),
+/// and metadata about the [session] and [device] used to collect the data.
+class DigitSpanTaskData {
+  /// Data for all trials
+  late final List<Trial> trials;
+
+  /// Metadata about the session
+  late final Session session;
+
+  /// Metadata about the device on which the data was collected
+  late final Device device;
+
+  DigitSpanTaskData({
+    required this.trials,
+    required this.session,
+    required this.device,
+  });
+
+  @override
+  String toString() {
+    final representation = 'Session data:'
+        '\n${session.toString()}'
+        '\nDevice data:'
+        '\n${device.toString()}'
+        '\nTrials data:'
+        '\n${trials.toString()}';
+    return representation;
+  }
+}

test/src/digit_span_task/components/data/digit_span_task_data_test.dart

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+import 'package:cognitive_data/cognitive_data.dart';
+import 'package:digit_span_tasks/src/digit_span_task/components/data/digit_span_task_data.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  test(
+    "DigitSpanTaskData.toString returns correct representation",
+    () {
+      TestWidgetsFlutterBinding.ensureInitialized();
+
+      /// arrange
+      /// session
+      final Session session = Session(
+          participantID: '101',
+          sessionID: '001',
+          startTime: DateTime.now(),
+          endTime: DateTime.now());
+
+      /// device
+      final Device device = Device(participantID: '101', sessionID: '001');
+
+      /// list trial
+      final List<Trial> trials = <Trial>[
+        Trial(
+            participantID: '101',
+            sessionID: '001',
+            trialType: TrialType.practice,
+            stim: '456',
+            response: '123'),
+        Trial(
+            participantID: '102',
+            sessionID: '002',
+            trialType: TrialType.practice,
+            stim: '789',
+            response: '987'),
+      ];
+
+      /// DigitSpanTaskData
+      DigitSpanTaskData data = DigitSpanTaskData(
+        session: session,
+        device: device,
+        trials: trials,
+      );
+
+      /// expected
+      final expectedRepr = 'Session data:'
+          '\n${session.toString()}'
+          '\nDevice data:'
+          '\n${device.toString()}'
+          '\nTrials data:'
+          '\n${trials.toString()}';
+
+      /// act
+      /// tostring
+      final String actualRepr = data.toString();
+
+      /// assert
+      expect(actualRepr, expectedRepr);
+    },
+  );
+}