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powershellartillery

null-valued expression while executing artillery.io tests as Diagnostics.ProcessStartInfo

I have test written in artillery.io (yaml file):

config:
  target: "http://localhost:3000/"
  phases:
    - duration: "{{duration}}" #//10
      arrivalRate: 1
 
scenarios:
  - name: "Emit an event"
    engine: socketio
    flow:
      - loop:
          - emit:
              channel: "chat
               message"
              data: "{{data}}"
          - think: 1
        count: "{{count}}"

I have written powershell script for automatic run many scenarios:

##ArtilleryIo platform test

$no_of_requests = 1,2,25,100,500
$no_of_users = 1,2,10,100,500,1000
$content_length = 1,2,10,100,500,1000,10000

$args=""
foreach($request in $no_of_requests){
    
    foreach($len in $content_length)
    {
        foreach($user in $no_of_users)
        {
            try{
                $integer_len = [int]$len
                $generatedData = -join ((65..90)+(97..122) | Get-Random -Count $integer_len | % {[char]$_})
                $path = "artillery run --output test-run-report.json C:\Users\patryk\socket_io\server\tests\load-test.yml"
                $waitForExit = $true
                $psi = new-object "Diagnostics.ProcessStartInfo"
                $psi.FileName = "artillery" 
                $integer_user = [int]$user
                $integer_req = [int]$request
                $pathToSave = "C:\Users\patryk\socket_io\server\tests\req_$request\len_$len-user_$user"
                $dirComm = "mkdir $pathToSave"
                #Write-Host "dir comm: " $dirComm
                Invoke-Expression $dirComm
                $args = ' run --variables ''{ \"duration\": '+$integer_user+', \"data\": \"'+$generatedData+'\", \"count\": '+$integer_req+ '}'' --output '+$pathToSave+'\test-run-report.json C:\Users\patryk\socket_io\server\tests\load-test.yml' #-f $integer_user,$generatedData,$integer_req,$pathToSave
                $psi.Arguments = $args
                $proc = [Diagnostics.Process]::Start($psi)
                if ( $waitForExit ) {
                    #Write-Host $PWD
                    $proc.WaitForExit();
                    $stdout = $proc.StandardOutput.ReadToEnd()
                    $stderr = $proc.StandardError.ReadToEnd()
                    Write-Host "stdout: $stdout"
                    Write-Host "stderr: $stderr"
                }
            }
            catch {
                Write-Host "An error occurred:"
                Write-Host $_
                
                Write-Host "Error occured with: user: $user, data: $generatedData, noOfRequests: $request, args: $args"
            }
                
        }
    }
}

During executing my script in see in the console:

An error occurred:
You cannot call a method on a null-valued expression.
Error occured with: user: 1, data: b, noOfRequests: 1, args:  run --variables '{ \"duration\": 1, \"data\": \"b\", \"count\": 1}' --output C:\Users\patryk\socket_io\server\tests\req_1\len_1-user_1\test-run-report.json C:\Users\patryk\socket_io\server\tests\load-test.yml

but if i paste command artillery run --variables '{ \"duration\": 1, \"data\": \"b\", \"count\": 1}' --output C:\Users\patryk\socket_io\server\tests\req_1\len_1-user_1\test-run-report.json C:\Users\patryk\socket_io\server\tests\load-test.yml directly to console and execute my test works. Can you tell me what is wrong? I have read that this exception indicates that something is null (like null pointer exception) but still couldn't fix it. Regards

Solution

    • Your primary problem is that you neglected to set the $psi.RedirectStandardOut and $psi.RedirectStandardError properties to $true, which resulted in no output getting collected, in turn causing $proc.StandardOutput and $proc.StandardError to be $null, which therefore caused the error you saw.

    • Secondarily, $args = ' run --variables ''{ \"dur... cannot work, because on process command lines only "..." rather than '...' quoting may generally be used.

    $arguments = @"
run --variables "{ \"duration\": $integer_user, \"data\": \"$generatedData\", \"count\": $integer_req }" --output $pathToSave\test-run-report.json C:\Users\patryk\socket_io\server\tests\load-test.yml
"@