Reorganize tests

- Pester source code moved to `test/Pester`, deleted `ext-src`.
- Pester tests (.ps1 files) moved to `test/powershell`
- xUnit tests (.cs files) moved to `test/csharp`
- Third-party script test moved to `test/shebang`

test/powershell/Start-Process.Tests.ps1

@@ -0,0 +1,74 @@
+$here = Split-Path -Parent $MyInvocation.MyCommand.Path
+. $here/Test-Common.ps1
+
+Describe "Start-Process" {
+    $pingCommand = (Get-Command -CommandType Application ping)[0].Definition
+    $pingDirectory = Split-Path $pingCommand -Parent
+    $tempFile = "$(GetTempDir)/PSTest"
+    $assetsFile = $here + "/assets/SortTest.txt"
+    $windows = IsWindows
+    if ($windows)
+    {
+        $pingParam = "localhost -n 4"
+    }
+    else
+    {
+        $pingParam = "localhost -c 4"
+    }
+
+    It "Should process arguments without error" {
+        $process = Start-Process ping -ArgumentList $pingParam -PassThru
+
+        $process.Length      | Should Be 1
+        $process.Id          | Should BeGreaterThan 1
+        $process.ProcessName | Should Be "ping"
+    }
+
+    It "Should work correctly when used with full path name" {
+        $process = Start-Process $pingCommand -ArgumentList $pingParam -PassThru
+
+        $process.Length      | Should Be 1
+        $process.Id          | Should BeGreaterThan 1
+        $process.ProcessName | Should Be "ping"
+    }
+
+    It "Should invoke correct path when used with FilePath argument" {
+        $process = Start-Process -FilePath $pingCommand -ArgumentList $pingParam -PassThru
+
+        $process.Length      | Should Be 1
+        $process.Id          | Should BeGreaterThan 1
+        $process.ProcessName | Should Be "ping"
+    }
+
+    It "Should wait for command completion if used with Wait argument" {
+        $process = Start-Process ping -ArgumentList $pingParam -Wait -PassThru
+    }
+
+    It "Should work correctly with WorkingDirectory argument" {
+        $process = Start-Process ping -WorkingDirectory $pingDirectory -ArgumentList $pingParam -PassThru
+
+        $process.Length      | Should Be 1
+        $process.Id          | Should BeGreaterThan 1
+        $process.ProcessName | Should Be "ping"
+    }
+
+    It "Should should handle stderr redirection without error" {
+        $process = Start-Process ping -ArgumentList $pingParam -PassThru -RedirectStandardError $tempFile
+
+        $process.Length      | Should Be 1
+        $process.Id          | Should BeGreaterThan 1
+        $process.ProcessName | Should Be "ping"
+    }
+
+    It "Should should handle stdout redirection without error" {
+        $process = Start-Process ping -ArgumentList $pingParam -Wait -RedirectStandardOutput $tempFile
+        $dirEntry = dir $tempFile
+	$dirEntry.Length | Should BeGreaterThan 0
+    }
+
+    It "Should should handle stdin redirection without error" {
+        $process = Start-Process sort -Wait -RedirectStandardOutput $tempFile -RedirectStandardInput $assetsFile
+        $dirEntry = dir $tempFile
+	$dirEntry.Length | Should BeGreaterThan 0
+    }
+}