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/csharp/test_SecuritySupport.cs

@@ -0,0 +1,35 @@
+using Xunit;
+using System;
+using System.Management.Automation;
+
+namespace PSTests
+{
+    public static class SecuritySupportTests
+    {
+        [Fact]
+        public static void TestScanContent()
+        {
+            Assert.Equal(AmsiUtils.ScanContent("", ""), AmsiUtils.AmsiNativeMethods.AMSI_RESULT.AMSI_RESULT_NOT_DETECTED);
+        }
+
+        [Fact]
+        public static void TestCurrentDomain_ProcessExit()
+        {
+            Assert.Throws<PlatformNotSupportedException>(delegate {
+                    AmsiUtils.CurrentDomain_ProcessExit(null, EventArgs.Empty);
+                });
+        }
+
+        [Fact]
+        public static void TestCloseSession()
+        {
+            AmsiUtils.CloseSession();
+        }
+
+        [Fact]
+        public static void TestUninitialize()
+        {
+            AmsiUtils.Uninitialize();
+        }
+    }
+}