Struggling to identify the error while utilizing Jasmine's throwError function

Question

Struggling to identify the error while utilizing Jasmine's throwError function

I am relatively new to using Jasmine and have been experimenting with the toThrowError() function. However, I can't seem to get my test to pass successfully.

In one of my functions, I purposely throw an error:

test.service.ts

test(list:{}){ 
    if(list == null){
        throw new TypeError();
    }
    else{
        // do something...
    }
}

Here is my test code:

it('should throw an error', inject()
    [
        TestService
    ],
    (
        testService: TestService
    ) => {
        let test = testService.test(null);
        expect(test).toThrowError(TypeError);
    }
);

Unfortunately, my test is failing with an Uncaught TypeError (I have tried calling it within a try-catch block).

angular typescript jasmine

Answer 1

Answer №1

It's important to note that if you expect a function to throw an error when called with null, you need to pass the function itself to the expect statement. As it stands, the current setup is not causing the error to be thrown as expected.

expect(() => testService.test(null)).toThrowError(TypeError);

To clarify further, the line of code below in your test:

let test = testService.test(null);

essentially calls the test function with null, resulting in a TypeError. However, because this action is outside of the expect block, Jasmine interprets it as an "uncaught" error. Once the error is thrown, nothing else in the subsequent

expect(test).toThrowError(TypeError);

line gets executed.

In order for the test to work properly, you should provide a function to the expect statement. This way, when Jasmine runs the function, the expected TypeError will be thrown, meeting the condition set by toThrowError(TypeError).

Answer 2

It's important to note that if you expect a function to throw an error when called with null, you need to pass the function itself to the expect statement. As it stands, the current setup is not causing the error to be thrown as expected.

expect(() => testService.test(null)).toThrowError(TypeError);

To clarify further, the line of code below in your test:

let test = testService.test(null);

essentially calls the test function with null, resulting in a TypeError. However, because this action is outside of the expect block, Jasmine interprets it as an "uncaught" error. Once the error is thrown, nothing else in the subsequent

expect(test).toThrowError(TypeError);

line gets executed.

In order for the test to work properly, you should provide a function to the expect statement. This way, when Jasmine runs the function, the expected TypeError will be thrown, meeting the condition set by toThrowError(TypeError).

Answer 3

Answer №2

One way to handle errors with a spy is by throwing the error directly from the spy itself, as shown here.
Prior to throwing the error, make sure you have set up your expectations accordingly.
```
spyOn(foo, "setBar").and.throwError("quux");
```

Answer 4

One way to handle errors with a spy is by throwing the error directly from the spy itself, as shown here.
Prior to throwing the error, make sure you have set up your expectations accordingly.
```
spyOn(foo, "setBar").and.throwError("quux");
```

Struggling to identify the error while utilizing Jasmine's throwError function

Answer №1

Answer №2

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