Exploring how to successfully test the parsing of a string using JSON.parse in Jest

Question

Exploring how to successfully test the parsing of a string using JSON.parse in Jest

Currently, I am in the process of creating unit tests for an API.

In a scenario where I implement the following code:

const apiResponse:object = JSON.parse(body)
expect(apiResponse).toHaveProperty('error')

If the API does not return JSON data, an error message is displayed:

SyntaxError: Unexpected token p in JSON at position 0 at JSON.parse ()

Instead of encountering errors during testing, I would prefer my test to fail if the JSON parsing fails.

I am looking for a jest test that can verify:
Can the string received be parsed as valid JSON?

javascript json typescript api jestjs

Answer 1

Answer №1

I managed to tackle this issue by incorporating a helpful function I stumbled upon here

const validateJSON = (str:string) => {
    try {
        const json = JSON.parse(str);
        if (Object.prototype.toString.call(json).slice(8,-1) !== 'Object') {
        return false
        }
    } catch (e) {
        return false
    }
    return true
}

Subsequently, I could execute the following:

expect(validateJSON(body)).toBe(true)

Answer 2

I managed to tackle this issue by incorporating a helpful function I stumbled upon here

const validateJSON = (str:string) => {
    try {
        const json = JSON.parse(str);
        if (Object.prototype.toString.call(json).slice(8,-1) !== 'Object') {
        return false
        }
    } catch (e) {
        return false
    }
    return true
}

Subsequently, I could execute the following:

expect(validateJSON(body)).toBe(true)

Answer 3

Answer №2

To ensure that JSON parsing does not throw an error, you can utilize Jest's .not.toThrow() method.

Check out this custom example demonstrating how to assert that an object can be parsed into valid JSON:

it("Verifies metadata object can be converted to valid JSON", () => {
    const meta = articleMetaData(article);

    const parseJson = () => {
        const json = JSON.stringify(meta);
        JSON.parse(json);
    };

    expect(parseJson).not.toThrow();
});

If, for instance, the object exhibited a circular structure like so:

var obj = {
  a: "foo",
  b: obj
}

The test would result in failure:

The function was expected not to generate an error.
Instead, it produced:
    TypeError: Converting circular structure to JSON

Answer 4

To ensure that JSON parsing does not throw an error, you can utilize Jest's .not.toThrow() method.

Check out this custom example demonstrating how to assert that an object can be parsed into valid JSON:

it("Verifies metadata object can be converted to valid JSON", () => {
    const meta = articleMetaData(article);

    const parseJson = () => {
        const json = JSON.stringify(meta);
        JSON.parse(json);
    };

    expect(parseJson).not.toThrow();
});

If, for instance, the object exhibited a circular structure like so:

var obj = {
  a: "foo",
  b: obj
}

The test would result in failure:

The function was expected not to generate an error.
Instead, it produced:
    TypeError: Converting circular structure to JSON

Exploring how to successfully test the parsing of a string using JSON.parse in Jest

Answer №1

Answer №2

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