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/DotNetAPI.Tests.ps1

@@ -0,0 +1,25 @@
+Describe "DotNetAPI" {
+    $posh_E  = 2.718281828459045
+    $posh_pi = 3.14159265358979
+
+    It "Should be able to use static .NET classes and get a constant" {
+        [System.Math]::E  | Should Match $posh_E.ToString()
+        [System.Math]::PI | Should Match $posh_pi.ToString()
+    }
+
+    It "Should be able to invoke a method" {
+        [System.Environment]::GetEnvironmentVariable("PATH") | Should Be $env:PATH
+    }
+
+    It "Should not require 'system' in front of static classes" {
+        [Environment]::CommandLine | Should Be ([System.Environment]::CommandLine)
+
+        [Math]::E | Should Be ([System.Math]::E)
+    }
+
+    It "Should be able to create a new instance of a .Net object" {
+        [System.Guid]$guidVal = [System.Guid]::NewGuid()
+
+        $guidVal.GetType().Name | Should Be "Guid"
+    }
+}