Mastering RxJs Observables: Effective Testing Tips

Table of Contents

1. Introduction
2. The Structure Problem of Testing Observables
   • Understanding Observable Structure
   • The Challenges of Testing Observables
3. The Marble Testing Issue
   • Multiple Libraries and APIs
   • Syntax Complexity
   • Lack of Documentation
   • Testing Implementation Details
4. Testing Observables with Auto Spies
   • The Three Parts of a Test
   • Configuring Fake Inputs with Auto Spies
   • Using the Action-Verification Approach
5. Benefits of Auto Spies and Observer Spy
   • Flattening the Test Structure
   • Handling Multiple Values Efficiently
   • Avoiding Memory Leaks
6. Applying Auto Spies and Observer Spy in Example Code
   • Refactoring the Code to Use Observer Spy
   • Using the Auto Unsubscribe Function
7. Additional Considerations and Advanced Topics
   • Just Enough Principle
   • Test Per Link in the Chain
   • Testing Effects in NgRx
8. Conclusion

Testing Observables Effectively without Marbles

Testing observables can be a challenging task, particularly when it comes to understanding their structure and accurately verifying their behavior. Additionally, the popular approach of using marble tests introduces further complexity. In this article, we will explore a more efficient and Simplified method of testing observables without relying on marbles.

Introduction

Testing plays a crucial role in software development, ensuring that code behaves as expected and meets the required specifications. However, testing observables can be particularly difficult due to their unique characteristics and operational complexities. It is essential to find effective strategies and tools that simplify the testing process, without sacrificing accuracy or efficiency.

The Structure Problem of Testing Observables

When testing observables, one of the first challenges is understanding their structure. Observables are composed of multiple operators, each impacting the data flow in unique ways. Determining Where To start and what to test can be confusing without a clear understanding of the observable's structure.

To address this issue, it is helpful to break down the test into three distinct parts: setup, action, and verification. In the setup phase, fake inputs are configured to simulate the necessary conditions for the test. The action phase involves executing the function or method being tested. The verification phase compares the actual output of the test with the expected results.

The Marble Testing Issue

Marble testing has often been touted as the standard approach for testing observables. However, it introduces additional challenges and complexities that can hinder the testing process.

Multiple Libraries and APIs

When researching how to test observables, You may come across various libraries and APIs, each offering their own approach to marble testing. This plethora of options can lead to confusion and make it challenging to choose the right library or API for your testing needs.

Syntax Complexity

Marble testing utilizes a cryptic language to define the behavior of observables and their emissions. The syntax often includes symbols such as dashes (-) to represent virtual frames of time and can be difficult to understand and work with. As a result, developers may find themselves struggling to learn and write tests using this syntax.

Lack of Documentation

Another drawback of marble testing is the lack of comprehensive documentation, especially for popular libraries like Jasmine Marbles. Developers often need to resort to reading source code to understand how the libraries work and troubleshoot any issues. This reliance on source code hinders the speed and efficiency of test development.

Testing Implementation Details

One of the limitations of marble testing is that it focuses on testing implementation details rather than the desired outcomes. Marble tests require precise knowledge of how much time has passed between emissions, which can lead to fragile tests that break when implementation details change. In contrast, developers should aim to test the outcomes and expected behavior of observables rather than specific implementation details.

Testing Observables with Auto Spies

To overcome the challenges posed by marble testing, we can leverage tools like Auto Spies and Observer Spy. Auto Spies simplifies the process of configuring fake inputs for observables, while Observer Spy provides an elegant solution for capturing and verifying observable outputs.

The Three Parts of a Test

When testing observables with Auto Spies and Observer Spy, it is essential to follow the three-part structure of a test: setup, action, and verification. In the setup phase, we configure the fake inputs and Create the necessary spies. The action phase involves executing the function or method being tested. Finally, in the verification phase, we capture the actual output and compare it with the expected results.

Configuring Fake Inputs with Auto Spies

Auto Spies is a library that automates the process of creating spies, helping developers generate them Instantly and benefit from strong typing, making refactoring easier. By using the provideAutoSpy function, we can create an auto spy for a service, allowing us to configure and intercept its methods for testing purposes. Additionally, Auto Spies provides helpful methods like nextWith to define the behavior and emulated output of the auto spy.

Using the Action-Verification Approach

Observer Spy simplifies the process of capturing real outputs from observables without subscribing and nesting code. By using the subscribeSpy2 method, we can replace the traditional subscription with an observer spy. This simplifies the testing structure, improves readability, and overcomes the challenges associated with multiple values and memory leaks often encountered when using traditional subscriptions.

Benefits of Auto Spies and Observer Spy

Using Auto Spies and Observer Spy in testing observables comes with several advantages:

Flattening the Test Structure

Auto Spies helps flatten the test structure by automating the process of creating spies without the need for manual subscription. This results in cleaner and more readable tests, allowing developers to focus on the essential aspects of the test.

Handling Multiple Values Efficiently

Observer Spy simplifies the process of handling multiple values emitted by an observable. Instead of relying on complex operators and nested code, developers can use Observer Spy's Helper methods like getLastValue or getFirstValue to capture the desired outputs and verify their correctness. This approach simplifies testing scenarios with multiple emissions and ensures efficient and accurate tests.

Avoiding Memory Leaks

Traditionally, if tests do not unsubscribe from observables, memory leaks can occur, leading to performance issues. By utilizing Observer Spy's AutoUnsubscribe function, developers can automatically unsubscribe from the observable, preventing memory leaks and ensuring optimal test performance.

Applying Auto Spies and Observer Spy in Example Code

To demonstrate the effectiveness of Auto Spies and Observer Spy, let's consider an example Scenario. Suppose we have a component called ImaginaryFriendsComponent, which has a method called getBestFriends. In this method, we retrieve a list of friends from a service and filter them to only include the best friends.

By utilizing Auto Spies, we can create an auto spy for the service and configure its getListOfFriends method to return fake data. Subsequently, by using Observer Spy, we can capture the output of the getBestFriends method and verify its correctness.

Additional Considerations and Advanced Topics

Apart from the fundamental principles of testing observables with Auto Spies and Observer Spy, there are advanced topics worth exploring, such as:

Just Enough Principle

The Just Enough Principle suggests testing observables for the necessary outcomes without diving into unnecessary implementation details. By following this principle, developers can write more reliable and maintainable tests that focus on the observable's behavior rather than its internal mechanisms.

Test Per Link in the Chain

In scenarios where observables contain several transformation operators or linked chains, it is essential to Apply the Test Per Link in the Chain principle. This approach involves testing each operator or link individually and ensuring that they behave as expected. By adopting this principle, developers can identify the cause of any failures or issues more precisely.

Testing Effects in NgRx

When working with NgRx, a state management library for Angular, testing effects is an essential aspect. By understanding how to integrate Auto Spies and Observer Spy within the NgRx framework, developers can effectively test and verify the behavior of their effects.

Conclusion

Testing observables effectively without relying on marbles is essential for efficient and accurate test development. By leveraging tools like Auto Spies and Observer Spy, developers can overcome the challenges associated with traditional marble testing. These tools simplify the test structure, handle multiple values efficiently, and ensure robust and reliable testing. With a solid understanding of the principles and techniques discussed in this article, developers can elevate their testing practices and deliver high-quality software products.