[stress testing] Improve scenario matrix edge case handling (#4504)

Author: benbp

eng/common/scripts/stress-testing/generate-scenario-matrix.ps1

@@ -39,12 +39,16 @@ function GenerateScenarioMatrix(
         $scenariosMatrix += $entry
     }
 
-    $valuesYaml = Get-Content -Raw (Join-Path (Split-Path $matrixFilePath) 'values.yaml')
-    $values = $valuesYaml | ConvertFrom-Yaml -Ordered
-    if (!$values) {$values = @{}}
+    $valuesConfig = Join-Path (Split-Path $matrixFilePath) 'values.yaml'
+    $values = [ordered]@{}
+    if (Test-Path $valuesConfig) {
+        $valuesYaml = Get-Content -Raw $valuesConfig
+        $values = $valuesYaml | ConvertFrom-Yaml -Ordered
+        if (!$values) {$values = @{}}
 
-    if ($values.ContainsKey('Scenarios')) {
-        throw "Please use matrix generation for stress test scenarios."
+        if ($values.ContainsKey('Scenarios')) {
+            throw "Please use matrix generation for stress test scenarios."
+        }
     }
 
     $values.scenarios = $scenariosMatrix

eng/common/scripts/stress-testing/stress-test-deployment-lib.ps1

@@ -248,7 +248,7 @@ function DeployStressPackage(
                 }
             }
         }
-        $genVal.scenarios = foreach ($scenario in $genVal.scenarios) {
+        $genVal.scenarios = @( foreach ($scenario in $genVal.scenarios) {
             $dockerPath = Join-Path $pkg.Directory $scenario.image
             if ("image" -notin $scenario) {
                 $dockerPath = $dockerFilePath
@@ -257,7 +257,7 @@ function DeployStressPackage(
                 $scenario.imageTag = $imageTag
             }
             $scenario
-        }
+        } )
 
         $genVal | ConvertTo-Yaml | Out-File -FilePath $genValFile
     }