我发现的解决方案是在测试中抽取2个按钮小部件，第一个调用我们正在测试的函数，第二个包含Navigator.of(context).pop()调用。第二个应该匹配函数的Navigator.of(context).pushNamed([route])中使用的任何路由。
下面是一个代码片段来澄清：

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('test function', (WidgetTester tester) async {
    // Build the widget that contains the button
    await tester.pumpWidget(MaterialApp(
      onGenerateRoute: (settings) {
        if (settings.name == "[route name used in function's pushNamed()]") {
          return MaterialPageRoute(builder: (context) => SecondPage());
        }
        return null;
      },
      home: Scaffold(
        body: Center(
          child: ElevatedButton(
            child: Text('Go to Second Page'),
            onPressed: () {
              // call function that's being tested here
            },
          ),
        ),
      ),
    ));

    // Tap the button to navigate to the SecondPage
    await tester.tap(find.text('Go to Second Page'));
    await tester.pumpAndSettle();

    // Tap the button to go back to the home page
    await tester.tap(find.text('Go Back'));
    await tester.pumpAndSettle();

    // add expect() here to check if the global variables were updated or not
  });
}

class SecondPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Second Page'),
      ),
      body: Center(
        child: ElevatedButton(
          child: Text('Go Back'),
          onPressed: () {
            // Navigator.of(context).pop(true); test 1
            // Navigator.of(context).pop(); test 2
          },
        ),
      ),
    );
  }
}