Best Practices for Enhancing Testability of Wrapper Methods

Question

Best Practices for Enhancing Testability of Wrapper Methods

Recently, I have implemented a practice in my tests where I encapsulate error messages and string manipulations into methods or variables to enhance the resilience of my tests in case the content of error messages changes in the future.

For instance, I would modify code like this:

try{
    someMethod();
}catch(e){
    throw new Error('error message.');
}

to something like this:

let errorMessage = 'error message';
...
try{
    someMethod();
}catch(e){
    throw new Error(errorMessage);
}

I apply similar modifications if the error message involves a variable or other dynamic elements.

My inquiry pertains to the best approach to achieve this in Typescript. In Java, I usually designate them as package-protected, but it appears that Jasmine does not have access to such methods when they are protected. I also experimented with making them static.

Is there a recommended strategy for handling this scenario?

unit-testing typescript jasmine

Answer 1

Answer №1

It's always beneficial to adopt best practices from various programming languages on certain occasions.

By creating custom exceptions, you can easily verify their type instead of relying on error strings, promoting consistency in error handling.

While this example may seem complex, it demonstrates the concept well (adapted from pages 163-168 of Pro Typescript).

We begin by defining a base CustomException class that implements the Error interface and serves as the foundation for all custom error types in our application.
An InvalidDateException is then created to represent a specific type of error, centralizing the error message within the application.
With this setup, we can easily identify different error types using an instanceof check, as shown in the catch statement example.
All custom exceptions are designed to align with the Error interface requirements, which include implementing name and toString() methods.

Code:

class CustomException implements Error {
    protected name = 'CustomException';

    constructor(public message: string) {
    }

    toString() {
        return this.name + ': ' + this.message;
    }
}

class InvalidDateException extends CustomException {
    constructor(public date: Date) {
        super('The date supplied was not valid: ' + date.toISOString());
        this.name = 'InvalidDateException';
    }
}

try {
    throw new InvalidDateException(new Date());
} catch (ex) {
    if (ex instanceof InvalidDateException) {
        alert(ex.toString());
    }
}

Answer 2

It's always beneficial to adopt best practices from various programming languages on certain occasions.

By creating custom exceptions, you can easily verify their type instead of relying on error strings, promoting consistency in error handling.

While this example may seem complex, it demonstrates the concept well (adapted from pages 163-168 of Pro Typescript).

We begin by defining a base CustomException class that implements the Error interface and serves as the foundation for all custom error types in our application.
An InvalidDateException is then created to represent a specific type of error, centralizing the error message within the application.
With this setup, we can easily identify different error types using an instanceof check, as shown in the catch statement example.
All custom exceptions are designed to align with the Error interface requirements, which include implementing name and toString() methods.

Code:

class CustomException implements Error {
    protected name = 'CustomException';

    constructor(public message: string) {
    }

    toString() {
        return this.name + ': ' + this.message;
    }
}

class InvalidDateException extends CustomException {
    constructor(public date: Date) {
        super('The date supplied was not valid: ' + date.toISOString());
        this.name = 'InvalidDateException';
    }
}

try {
    throw new InvalidDateException(new Date());
} catch (ex) {
    if (ex instanceof InvalidDateException) {
        alert(ex.toString());
    }
}

Best Practices for Enhancing Testability of Wrapper Methods

Answer №1

Similar questions

Creating effective puppeteer tests with reasonable expectations

Tips for extracting the value of T from a Promise<T>

Basic exam but located in a place that is not valid

View the generated tsconfig file after including { "extends": ... }

When importing a React Component with styling into the pages folder, it fails to function properly

How to turn off automatic password suggestions in Chrome and Firefox

Encountering a 'scheduler flush execution error' and an Uncaught TypeError due to VueJS and Axios integration

Determining object keys based on the values of other keys to customize functions

Tips for confining the draggable div within its container

What are some techniques to ensure null checking is enforced for objects that are nested within multiple layers

Using React with Typescript: Can the parent component access data fetched from a nested child component?

Tips for accessing the following element within an array using a for loop with the syntax for (let obj of objects)

Why is the variable suddenly a number when I clearly defined it as a string?

When in debug mode, the Unit Test Sessions Window automatically closes

Tips for managing the output of an asynchronous function in TypeScript

Best practices for effectively sharing TypeScript code across multiple Aurelia CLI projects

A Step-by-Step Guide on Updating Your Angular 7 Project to Angular Version

Differentiating TypeScript classes is important in situations where they would normally be treated as equivalent

What could be causing this object to be null or undefined when it's within an else if statement?

The service fails to recognize the ActivatedRoute