Скачать или смотреть Mastering Flutter Bloc Widget Testing: Finding Text Under an If Statement

Learn how to effectively perform widget testing in Flutter using `BlocBuilder` and `BlocProvider`. This guide will help you find specific text in your widgets based on state conditions.
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This video is based on the question https://stackoverflow.com/q/67600684/ asked by the user 'SilkeNL' ( https://stackoverflow.com/u/10878426/ ) and on the answer https://stackoverflow.com/a/67603050/ provided by the user 'SilkeNL' ( https://stackoverflow.com/u/10878426/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering Flutter Bloc Widget Testing: Finding Text Under an If Statement

Flutter’s state management system, particularly the Bloc pattern, provides developers with the tools they need to manage application states effectively. However, testing these states—especially when they involve conditions such as if statements—can be somewhat tricky. If you're struggling with widget testing for a class such as WelcomeScreen that utilizes a BlocBuilder, this post will guide you through the solution step-by-step.

The Problem

You have a Flutter widget, WelcomeScreen, which uses both BlocProvider and BlocBuilder. The widget displays certain information based on its state. The catch? You want to perform a widget test to find specific text only visible when the state is set to WelcomeLoadSuccessState. Here's a snippet of your WelcomeScreen:

[[See Video to Reveal this Text or Code Snippet]]

In your widget test, you have code that successfully locates the fallback text ("Something"), but you struggle to find the "Welcome user" text that appears only with the right state.

The Solution

The key to finding the "Welcome user" text lies in properly configuring your WelcomeBloc and ensuring that the right state is emitted during the test. Here's how you can achieve this:

Step 1: Modify the BlocProvider

You need to add an event to your WelcomeBloc when it's created within the BlocProvider. Change this line:

[[See Video to Reveal this Text or Code Snippet]]

to:

[[See Video to Reveal this Text or Code Snippet]]

This ensures that your bloc emits the necessary states for the test.

Step 2: Implement the Test Function

Here's how your updated test function might look:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Explained

Event Emission: The addition of ..add(WelcomeLoadRequestEvent(...)) ensures that the WelcomeBloc is correctly set up to emit the states we expect.

State Management: Using whenListen(...) allows you to control the flow of states emitted by your bloc. You simulate both loading and success states to simulate the user experience accurately.

Additional Tips

Separation of Concerns: For cleaner tests, consider separating the BlocProvider and BlocBuilder. This method will make it easier to mock the bloc and test individual components of your application.

Code Reusability: You can create helper functions to set up your test environments quickly and reuse them across different tests.

Conclusion

By following these steps, you can effectively locate the text within a widget under specific states when testing with the Flutter Bloc pattern. Mastering these techniques will significantly improve your ability to ensure that your app's UI behaves as expected in a variety of scenarios.

Happy Coding!