add support to install msu.

src/helpers/functions/Install-ChocolateyInstallPackage.ps1

@@ -76,5 +76,15 @@ param(
     }
   }
 
+  if($fileType -like 'msu') {
+
+    if ($overrideArguments) {
+      $msuArgs = "$file $additionalInstallArgs"
+    } else {
+      $msuArgs = "$file $silentArgs $additionalInstallArgs"
+    }
+    Start-ChocolateyProcessAsAdmin "$msuArgs" 'wusa.exe' -validExitCodes $validExitCodes
+  }
+
   write-host "$packageName has been installed."
 }

tests/unit/Install-ChocolateyInstallPackage.Tests.ps1

@@ -0,0 +1,18 @@
+$here = Split-Path -Parent $MyInvocation.MyCommand.Definition
+$common = Join-Path (Split-Path -Parent $here)  '_Common.ps1'
+$base = Split-Path -parent (Split-Path -Parent $here)
+
+. $common
+. "$base\src\helpers\functions\Install-ChocolateyInstallPackage.ps1"
+
+Describe "Install-ChocolateyInstallPackage" {
+    Context "When file type is msu" { 
+    Mock Start-ChocolateyProcessAsAdmin
+
+    Install-ChocolateyInstallPackage "package" "msu"
+    It "should be installed" {
+        Assert-MockCalled Start-ChocolateyProcessAsAdmin
+    }
+  }
+
+}