Error encountered while unit testing a class decorator with type mismatch

I have been tasked with implementing a class decorator that adds an "identify" class method, which returns a class name with the information passed in the decorator.
For example :

@identifier('example')
    class Test {}
    
    const test = new Test();
    console.log(test['identify']()); // Test-example  

When I console log, I get the expected result showing the class name and the string in brackets. However, the issue arises when running unit tests:

describe('identifier', () => {
    it('should return Test-example from identify', () => {
        @identifier('example')
        class Test {}
        const test = new Test();
        assert.strictEqual(test['identify'](), 'Test-example');
    });

    it('should return ClassA-prototype from identify', () => {
        @identifier('prototype')
        class ClassA {}
        const test = new ClassA();
        assert.strictEqual(test['identify'](), 'ClassA-prototype');
    })
});  

Decorator implementation :
Method 1 :

function identifier(...args: any): ClassDecorator {
    return function <TFunction extends Function>(
        target: TFunction
    ): TFunction | any {
        return target.name + "-" + args;
    };
}  

Method 2:

function identifier(passedInformation: string): any {
    return function (target) {
        return target.name + "-" + passedInformation;
    };
}  

Both functions seem correct, but they are both causing errors in junit.xml:

<testcase name="identifier should return Test-example from identify" time="0.0000" classname="should return Test-example from identify">
      <failure message="" type="TypeError"><![CDATA[TypeError: 
    at DecorateConstructor (node_modules\reflect-metadata\Reflect.js:544:31)
    at Object.decorate (node_modules\reflect-metadata\Reflect.js:130:24)
    at __decorate (test\index.ts:4:92)
    at C:\Users\artio\Desktop\6 Decorators\decorators\test\index.ts:81:20
    at Context.<anonymous> (test\index.ts:85:10)
    at processImmediate (internal/timers.js:439:21)]]></failure>
    </testcase>
    <testcase name="identifier should return ClassA-prototype from identify" time="0.0000" classname="should return ClassA-prototype from identify">
      <failure message="" type="TypeError"><![CDATA[TypeError: 
    at DecorateConstructor (node_modules\reflect-metadata\Reflect.js:544:31)
    at Object.decorate (node_modules\reflect-metadata\Reflect.js:130:24)
    at __decorate (test\index.ts:4:92)
    at C:\Users\artio\Desktop\6 Decorators\decorators\test\index.ts:93:22
    at Context.<anonymous> (test\index.ts:97:10)
    at processImmediate (internal/timers.js:439:21)]]></failure>
    </testcase>  

Can anyone identify the problem and suggest a solution? I am unable to complete the task due to these errors... It's worth mentioning that I cannot modify the unit tests, only the functions.

Answer №1

After encountering an error, I made some modifications to the function and ended up with the following solution:

function identifier(...args: any): ClassDecorator {
    return function <TFunction extends Function>(
        target: TFunction
    ): TFunction | any {
        var identify = target.prototype.identify;
        Object.defineProperty(target.prototype, 'identify', {
            value: function() {
                return target.name + "-" + args;
            }
        });
        return identify;
    };
}

I implemented the identify method as required by the task, returned it without any errors during unit tests or run time. It worked perfectly.

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