Test severity filtering of suppressed custom diagnostics

Co-authored-by: bergmeister <9250262+bergmeister@users.noreply.github.com>

Author: Copilot

Tests/Engine/CustomizedRule.tests.ps1

@@ -166,19 +166,49 @@ function ReportError {
 
     if ($ast.GetCommandName() -eq 'Invoke-Something') {
         New-Object -Typename 'Microsoft.Windows.PowerShell.ScriptAnalyzer.Generic.DiagnosticRecord' `
-            -ArgumentList 'This is an error', $ast.Extent, 'ReportError', Error, $ast.Extent.File, $null, $null
+            -ArgumentList 'This is an error', $ast.Extent, 'ReportError', Error, $ast.Extent.File, 'custom-id', $null
     }
 }
 '@
             $customRuleScriptPath = Join-Path $TestDrive 'SeverityRule.psm1'
             Set-Content -Path $customRuleScriptPath -Value $customRuleContent
+            (Get-ScriptAnalyzerRule -CustomRulePath $customRuleScriptPath).Severity | Should -Be 'Warning'
 
             $errors = Invoke-ScriptAnalyzer -ScriptDefinition 'Invoke-Something' -CustomRulePath $customRuleScriptPath -Severity Error
             $errors.Count | Should -Be 1
             $errors[0].Severity | Should -Be 'Error'
 
             $warnings = Invoke-ScriptAnalyzer -ScriptDefinition 'Invoke-Something' -CustomRulePath $customRuleScriptPath -Severity Warning
             $warnings.Count | Should -Be 0
+
+            $script = @'
+function Suppressed {
+    [Diagnostics.CodeAnalysis.SuppressMessageAttribute('ReportError', '', Justification = 'test justification')]
+    param()
+    Invoke-Something
+}
+Invoke-Something
+'@
+            foreach ($mode in 'SuppressedOnly', 'IncludeSuppressed') {
+                $parameters = @{
+                    ScriptDefinition = $script
+                    CustomRulePath = $customRuleScriptPath
+                    ErrorAction = 'Stop'
+                    $mode = $true
+                }
+
+                $errors = @(Invoke-ScriptAnalyzer @parameters -Severity Error)
+                $errors.Count | Should -Be $(if ($mode -eq 'SuppressedOnly') { 1 } else { 2 })
+                $suppressed = @($errors | Where-Object IsSuppressed)
+                $suppressed.Count | Should -Be 1
+                $suppressed[0].Severity | Should -Be 'Error'
+                $suppressed[0].RuleSuppressionID | Should -BeExactly 'custom-id'
+                $suppressed[0].Suppression | Should -HaveCount 1
+                $suppressed[0].Suppression[0].Justification | Should -BeExactly 'test justification'
+
+                $warnings = @(Invoke-ScriptAnalyzer @parameters -Severity Warning)
+                $warnings.Count | Should -Be 0
+            }
         }
 
         It "can suppress custom rule with rule name expression '<RuleNameExpression>'" -TestCases @(