Add -WhatIf switch to Start-Process cmdlet (#4735)

* Add -WhatIf switch to Start-Process cmdlet
* Add test for the -WhatIf switch 

* Added a test to ensure that using a whatif switch prevents the action from being performed.

* Incorporated code review comments

* merged two tests into one as suggested

* Included the error action at the end of the cmdlet

* Remove extra space before `StringUtil` and new line

* Renamed the resource string id ProcessStartInfo to StartProcessTarget

src/Microsoft.PowerShell.Commands.Management/commands/management/Process.cs

@@ -1658,7 +1658,7 @@ namespace Microsoft.PowerShell.Commands
     /// <summary>
     /// This class implements the Start-process command
     /// </summary>
-    [Cmdlet(VerbsLifecycle.Start, "Process", DefaultParameterSetName = "Default", HelpUri = "https://go.microsoft.com/fwlink/?LinkID=135261")]
+    [Cmdlet(VerbsLifecycle.Start, "Process", DefaultParameterSetName = "Default", SupportsShouldProcess = true, HelpUri = "https://go.microsoft.com/fwlink/?LinkID=135261")]
     [OutputType(typeof(Process))]
     public sealed class StartProcessCommand : PSCmdlet, IDisposable
     {
@@ -2051,6 +2051,9 @@ namespace Microsoft.PowerShell.Commands
                 startInfo.WindowStyle = _windowstyle;
             }
 
+            string targetMessage = StringUtil.Format(ProcessResources.StartProcessTarget, startInfo.FileName, startInfo.Arguments.Trim());
+            if (!ShouldProcess(targetMessage)) { return; }
+
             //Starts the Process
             Process process = Start(startInfo);
 

src/Microsoft.PowerShell.Commands.Management/resources/ProcessResources.resx

@@ -132,6 +132,9 @@
   <data name="ProcessNameForConfirmation" xml:space="preserve">
     <value>{0} ({1})</value>
   </data>
+  <data name="StartProcessTarget" xml:space="preserve">
+    <value>{0} {1}</value>
+  </data>
   <data name="CouldNotEnumerateModules" xml:space="preserve">
     <value>Cannot enumerate the modules of the "{0}" process.</value>
   </data>

test/powershell/Modules/Microsoft.PowerShell.Management/Start-Process.Tests.ps1

@@ -104,6 +104,16 @@ Describe "Start-Process" -Tags @("Feature") {
         $process.Name | Should Be "notepad"
         $process | Stop-Process
     }
+
+    It "Should be able to use the -WhatIf switch without performing the actual action" {
+        $pingOutput = Join-Path $TestDrive "pingOutput.txt"
+        { Start-Process -Wait $pingCommand -ArgumentList $pingParam -RedirectStandardOutput $pingOutput -WhatIf -ErrorAction Stop } | Should Not Throw
+        $pingOutput | Should Not Exist 
+    }
+
+    It "Should return null when using -WhatIf switch with -PassThru" {
+        Start-Process $pingCommand -ArgumentList $pingParam -PassThru -WhatIf | Should Be $null
+   }
 }
 
 Describe "Start-Process tests requiring admin" -Tags "Feature","RequireAdminOnWindows" {