Can not check the JSON value from the response body - postman

Question

I just started testing the api using the postman. I have come across one problem with the json path..
in json file I have code which looks like this
{
"users": [
{
"firstName": "UserOne",
"lastName": "One",
"subjectId": 1,
"id": 1
},
{
"firstName": "UserTwo",
"lastName": "Two",
"subjectId": 2,
"id": 2
},
{
"firstName": "UserThree",
"lastName": "Three",
"subjectId": 3,
"id": 3
}
],
"subjects": [
{
"id": 1,
"name": "SubOne"
},
{
"id": 2,
"name": "SubTwo"
},
{
"id": 3,
"name": "SubThree"
}
]
}
I start the json server with json-server --watch db.json
After that I send GET request using postman
Request URL http://localhost:3000/users
this is the body I get
[
{
"firstName": "UserOne",
"lastName": "One",
"subjectId": 1,
"id": 1
},
{
"firstName": "UserTwo",
"lastName": "Two",
"subjectId": 2,
"id": 2
},
{
"firstName": "UserThree",
"lastName": "Three",
"subjectId": 3,
"id": 3
}
]
I was trying to verify the firstName from the id 1 using the snippet code below
pm.test("Your test name", function () {
var jsonData = pm.response.json();
pm.expect(jsonData.users[0].firstName).to.eql('UserOne');
});
But the output was
FAIL Your test name | TypeError: Cannot read property '0' of undefined
I need help here because the json path users[0].firstName should give me the first index..

Answer 1

There is no key users in your response, so when you try to access the non-existed key, you will get error Cannot read property 'xxx' of undefined. To fix that, you just need:
pm.test("Your test name", function () {
var jsonData = pm.response.json();
pm.expect(jsonData[0].firstName).to.eql('UserOne');
});