Variables are not substituted in the Performance run from uploaded data.json , while working correctly in functional run

IrinaG1 · July 23, 2025, 5:20pm

Hi ,
I have a collection for performance testing , it reads data from the input data.json file , should be pretty much straight forward and works correctly in functional run , but when run performance test , variables values are not substituted .
Data in json looks like :

let initialData = 
    [
        {
            clientId:"",
            tenant:"",
            agents:[
                {
                agent_id:"",
                agent_token:""
                },
                {
                agent_id:"",
                agent_token:""
                },
                {
                agent_id:"",
                agent_token:""
                },
                {
                agent_id:"",
                agent_token:""
                },
                {
                agent_id:"",
                agent_token:""
                },
                {
                agent_id:"",
                agent_token:""
                },
                {
                agent_id:"",
                agent_token:""
                },
                {
                agent_id:"",
                agent_token:""
                },
                {
                agent_id:"",
                agent_token:""
                },
                {
                agent_id:"",
                agent_token:""
                }
            ],
            list:"",
            assets:[{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},
            {asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""},{asset_id:"",ip:""}],
            policies:[],
            rules:[],

        }]

In each request in the collection we fetch data in pre-requisite scripts with code

var stringAgents = JSON.stringify(pm.iterationData.get("agents"));
var agents = JSON.parse(stringAgents);
var agent_token = agents[0].agent_token;
pm.collectionVariables.set("agent_token", agent_token);
var stringAssets = JSON.stringify(pm.iterationData.get("assets"));
var assets = JSON.parse(stringAssets);
var asset_id = assets[0].asset_id;
console.log("asset_id:" + asset_id)
pm.collectionVariables.set("asset_id", asset_id);
var ip = assets[0].ip;
console.log("ip:" +ip)
pm.collectionVariables.set("ip", ip);
var tenant = pm.iterationData.get("tenant");
console.log("tenant:" +tenant)
pm.collectionVariables.set("tenant", tenant);
var list = pm.iterationData.get("list");
console.log("list"+list)
pm.collectionVariables.set("list", list);

But every time when I run performance test , with data.json , 20 UV users with rump up period , I got 100% fails because variables that are expected in the request headers and authentication are not substituted

While when functional run with same data.json file , all data is substituted correctly

Please advise what am i doing wrong

yonandualem · July 24, 2025, 6:33am

Try this fixes

Instead of setting collection variables, reference pm.iterationData directly in your request builder (URL, Headers, Body).
Example: If your request needs {{agent_token}} , change it to use {{$iterationData.agent_token}} or construct it in the pre-request script as an environment variable.
Use pm.environment.set("agent_token", agent_token) instead of collection variables.
Note: Environment variables are better scoped for VU runs than collection variables.
If possible, flatten your data.json so each row (object) contains all the variables needed for one iteration/VU. This avoids the need for dynamic variable-setting in scripts.

var agents = pm.iterationData.get("agents");
var agent_token = agents[0].agent_token;
pm.environment.set("agent_token", agent_token);

var assets = pm.iterationData.get("assets");
var asset_id = assets[0].asset_id;
pm.environment.set("asset_id", asset_id);
pm.environment.set("ip", assets[0].ip);

pm.environment.set("tenant", pm.iterationData.get("tenant"));
pm.environment.set("list", pm.iterationData.get("list"));

Then in your request, reference as {{agent_token}} , {{asset_id}} , etc.

IrinaG1 · July 24, 2025, 10:53am

Thank you @yonandualem unfortunately none of the proposed options worked , still functional runs are working fine but in performance variables are not substituted , tried with all possible options , environment , collection variables , global none was working .

yonandualem · July 24, 2025, 11:30am

Flatten your data.json so each variable you want to substitute is a top-level key with a simple value—no arrays or objects.
Reference variables directly in your requests:
Use {{$iterationData.agent_token}}, {{$iterationData.asset_id}}, etc., in your request URL, headers, body, and auth fields.
Remove all pre-request scripts related to variable setting for dynamic substitution. Only use pre-request scripts for logic/calculations not involving variable assignment for the current request.

[
  {
    "agent_token": "token1",
    "asset_id": "id1",
    "ip": "1.1.1.1",
    "tenant": "tenantA"
  },
  {
    "agent_token": "token2",
    "asset_id": "id2",
    "ip": "2.2.2.2",
    "tenant": "tenantB"
  }
]

Try this and let me know how it goes

IrinaG1 · July 24, 2025, 5:05pm

Thank you @yonandualem i made my data structure flat and simple substituted {{agent_token0}} , {{asset_id0}} and etc and it worked . But i am getting new problem with authorization for totally valid tokens I am receiving in response header WWW-Authenticate: Bearer error=“invalid_token”, error_description=“An error occurred while attempting to decode the Jwt: Signed JWT rejected: Another algorithm expected, or no matching key(s) found”, error_uri=“RFC 6750 - The OAuth 2.0 Authorization Framework: Bearer Token Usage”

I checked all possible trailing spaces in data and encoding issues nothing should cause problem

Any thoughts on that ?

yonandualem · July 24, 2025, 5:31pm

“Another algorithm expected, or no matching key(s) found”
The server expected your JWT to be signed with a specific algorithm (e.g., RS256 vs HS256), or it can’t find the public key to verify the signature.

Common Causes

Token Algorithm Mismatch

The JWT is signed with one algorithm (e.g., HS256) but the server expects another (e.g., RS256).

Incorrect Signing Key

The key used to sign the JWT doesn’t match the public key the server uses to verify it.

Malformed Token

The token is corrupted, has extra spaces, or is not well-formed (three parts separated by dots).

Expired or Invalid Token

The token is expired or otherwise not valid.

Test Data Copy/Paste Issues

Sometimes, copying tokens from Excel or JSON can introduce invisible characters or encoding problems. Even if you checked, try regenerating the tokens fresh.

IrinaG1 · July 24, 2025, 5:58pm

@yonandualem I have checked tokens in JWT.io and they are valid

IrinaG1 · July 24, 2025, 6:25pm

Thank you @yonandualem for help now evrything works

yonandualem · July 24, 2025, 6:38pm

Glad I helped. Cheers!

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Variables are not substituted in the Performance run from uploaded data.json , while working correctly in functional run

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