Add UI Tests for CurrencyDropdown Widget

test/features/currency/currency_dropdown_test.dart

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+import 'package:didpay/features/currency/currency_dropdown.dart';
+import 'package:didpay/features/payment/payment_amount_state.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import '../../helpers/test_data.dart';
+import '../../helpers/widget_helpers.dart';
+
+void main() async {
+  await TestData.initializeDids();
+
+  final testOffering = TestData.getOfferingsMap(payoutCurrencies: ['EUR', 'USD']);
+  final mockState = ValueNotifier<PaymentAmountState?>(
+    PaymentAmountState(
+      offeringsMap: testOffering,
+      selectedOffering: testOffering.values.first.first,
+    ),
+  );
+
+  Widget currencyDropdownTestWidget(String testCurrency) {
+    return WidgetHelpers.testableWidget(
+      child: CurrencyDropdown(
+        paymentCurrency: testCurrency,
+        state: mockState,
+      ),
+    );
+  }
+
+  testWidgets('should display the initial currency in CurrencyDropdown', (tester) async {
+    const testCurrency = 'USD';    
+    await tester.pumpWidget(currencyDropdownTestWidget(testCurrency));
+
+    expect(find.text(testCurrency), findsOneWidget);
+  });
+
+  testWidgets('should open Select Currency modal on tap in CurrencyDropdown', (tester) async {
+    const testCurrency = 'USD';    
+    await tester.pumpWidget(currencyDropdownTestWidget(testCurrency));
+
+    await tester.tap(find.text(testCurrency));
+    await tester.pumpAndSettle();
+
+    expect(find.text('Select currency'), findsOneWidget);
+  });
+
+  testWidgets('should update PaymentAmountState when a new offering is selected in CurrencyDropdown', (tester) async {
+    const testCurrency = 'EUR';
+    await tester.pumpWidget(currencyDropdownTestWidget(testCurrency));
+
+    await tester.tap(find.text(testCurrency));
+    await tester.pumpAndSettle();
+
+    const selectedCurrency = 'EUR';
+    await tester.tap(find.text(selectedCurrency));
+
+    await tester.pumpAndSettle();
+
+    expect(mockState.value?.payoutCurrency, selectedCurrency);
+  });
+}