JSON object with Jest tests in node.js project not being parsed properly

Question

I have an object with the following interface:

export interface range {
  max: number,
  min: number
}

That I'm returning from a GET call - the function that is called is listed below.

export async function testHandler() {
  let result : range = {
    min: 101, 
    max: 202
  };
 
  return {
    body: JSON.stringify({
      data: result
    }),
    statusCode: 200
  };
}

The idea is that I want to return & parse an instance of the range object to my Jest tests, which are shown below:

import {  testHandler, range } from "..";

describe("TestEnv", () => {
  const expectedResponseShape = {
    body: expect.any(String),
    statusCode: expect.any(Number)
  };
 
describe("Test Range Test", () => {
it("should return the correct data shape: min and max, >= 0", async () => {
  const response = await testHandler();
  //make sure we're getting a response with an HTTP body
  expect(response).toEqual(expectedResponseShape);
  expect(response.statusCode).toEqual(200);

  let r : range = JSON.parse(JSON.stringify(response.body));
  expect(r).not.toBeUndefined();

  console.log(`range: ${r}`);
  console.log(`range.min: ${r.min}`);
  console.log(`range.max: ${r.max}`);


  for(var propName in r) {
    if(r.hasOwnProperty(propName)) {
        console.log(`propname ${propName} =:  ${r[propName]}`);   
    }
  }
});

});

So this is where things get really weird. For the life of me I can't figure out why the r object won't parse. The output from the logs is below:

Test Range Test
      ✓ should return the correct data shape: min and max, >= 0 (46ms)

  console.log 
          range: {"data":{"min":101,"max":202}}

  console.log 
    range.min: undefined

  console.log 
    range.max: undefined

  console.log 
    propname 0 =:  {

  console.log 
    propname 1 =:  "

  console.log 
    propname 2 =:  d

  console.log 
    propname 3 =:  a

  console.log 
    propname 4 =:  t

  console.log 
    propname 5 =:  a

and so on until

 console.log 
    propname 25 =:  2

  console.log 
    propname 26 =:  0

  console.log 
    propname 27 =:  2

  console.log 
    propname 28 =:  }

  console.log 
    propname 29 =:  }

So the data of the object (which is {min: 101, max:202} ) seems to be coming in ok, but does not seem to be parsed properly. What I would like is a final object in the tests that will be able to read a result r of type range, and be able to read its properties with r.min and r.max.

The answer is probably obvious, but what am I doing wrong?

Gabriele Petrioli · Accepted Answer · 2021-02-09 21:40:05Z

1

First of all, the "range" is in the data prop, and not directly in the body of the response.

Secondly you do JSON.stringify on the response.body which is already a string.

So, use

let r : range = JSON.parse(response.body).data;

the weird logs are also due to the extra JSON.stringify of the response.body. Your r ends up being a string and the for .. in is iterating it as an array of chars.

answered Feb 9, 2021 at 21:40

Gabriele Petrioli

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