Feature/update max value

lib/src/util/datasets_util.dart

@@ -17,15 +17,11 @@ class DatasetsUtil {
 
   /// Get maximum value of [datasets].
   static int getMaxValue(Map<DateTime, int>? datasets) {
-    int result = 0;
-
-    datasets?.forEach((date, value) {
-      if (value > result) {
-        result = value;
-      }
-    });
+    if (datasets == null || datasets.isEmpty) {
+      return 0; // Return 0 for empty or null datasets
+    }
 
-    return result;
+    return datasets.values.reduce((max, value) => value > max ? value : max);
   }
 
   /// Get color from [colorsets] using [dataValue].

test/src/util/datasets_util_test.dart

@@ -0,0 +1,33 @@
+import 'package:flutter_heatmap_calendar/src/util/datasets_util.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  test('getMaxValue returns the maximum value from the dataset', () {
+    final Map<DateTime, int> datasets = {
+      DateTime(2023, 9, 1): 10,
+      DateTime(2023, 9, 2): 20,
+      DateTime(2023, 9, 3): 5,
+      DateTime(2023, 9, 4): 15,
+    };
+
+    final result = DatasetsUtil.getMaxValue(datasets);
+
+    expect(result, 20); // The maximum value in the dataset is 20
+  });
+
+  test('getMaxValue handles an empty dataset and returns 0', () {
+    final Map<DateTime, int> emptyDataset = {};
+
+    final result = DatasetsUtil.getMaxValue(emptyDataset);
+
+    expect(result, 0); // The dataset is empty, so the result should be 0
+  });
+
+  test('getMaxValue handles a null dataset and returns 0', () {
+    const Map<DateTime, int>? nullDataset = null;
+
+    final result = DatasetsUtil.getMaxValue(nullDataset);
+
+    expect(result, 0); // The dataset is null, so the result should be 0
+  });
+}