Improve speed of Test-IsNanoServer function

DscResources/CommonResourceHelper.psm1

@@ -8,23 +8,26 @@ function Test-IsNanoServer
     [CmdletBinding()]
     param ()
 
-    $isNanoServer = $false
-
-    if (Test-CommandExists -Name 'Get-ComputerInfo')
+    $serverLevelsRegKey = 'HKLM:\Software\Microsoft\Windows NT\CurrentVersion\Server\ServerLevels'
+    
+    if (Test-Path -Path $serverLevelsRegKey)
     {
-        $computerInfo = Get-ComputerInfo -ErrorAction 'SilentlyContinue'
-
-        if ($null -ne $computerInfo)
+        $serverLevels = Get-ItemProperty -Path $serverLevelsRegKey
+        
+        if ($serverLevels.NanoServer -eq 1)
         {
-            $computerIsServer = 'Server' -ieq $computerInfo.OsProductType
-
-            if ($computerIsServer)
-            {
-                $isNanoServer = 'NanoServer' -ieq $computerInfo.OsServerLevel
-            }
+            $isNanoServer = $true
+        }
+        else
+        {
+            $isNanoServer = $false
         }
     }
-
+    else
+    {
+        $isNanoServer = $false
+    }
+
     return $isNanoServer
 }
 

README.md

@@ -586,6 +586,7 @@ The following parameters will be the same for each process in the set:
   troubleshoot issues with the test HttpListener objects in the future.
   Specifically fixes
   [Issue #142](https://github.com/PowerShell/PSDscResources/issues/142)
+* Improved speed of Test-IsNanoServer function
 
 ### 2.11.0.0
 

Tests/Unit/CommonResourceHelper.Tests.ps1

@@ -14,136 +14,54 @@ Describe 'CommonResourceHelper Unit Tests' {
     InModuleScope 'CommonResourceHelper' {
         Describe 'Test-IsNanoServer' {
             $testComputerInfoNanoServer = @{
-                OsProductType = 'Server'
-                OsServerLevel = 'NanoServer'
+                NanoServer = 1
             }
 
             $testComputerInfoServerNotNano = @{
-                OsProductType = 'Server'
-                OsServerLevel = 'NotNano'
             }
 
-            $testComputerInfoNotServer = @{
-                OsProductType = 'NotServer'
-                OsServerLevel = 'NotNano'
-            }
-
-            Mock -CommandName 'Test-CommandExists' -MockWith { return $true }
-            Mock -CommandName 'Get-ComputerInfo' -MockWith { return $testComputerInfoNanoServer }
-
-            Context 'Get-ComputerInfo command exists and succeeds' {
-                Context 'Computer OS type is Server and OS server level is NanoServer' {
-                    It 'Should not throw' {
-                        { $null = Test-IsNanoServer } | Should -Not -Throw
-                    }
-
-                    It 'Should test if the Get-ComputerInfo command exists' {
-                        $testCommandExistsParameterFilter = {
-                            return $Name -eq 'Get-ComputerInfo'
-                        }
-
-                        Assert-MockCalled -CommandName 'Test-CommandExists' -ParameterFilter $testCommandExistsParameterFilter -Exactly 1 -Scope 'Context'
-                    }
-
-                    It 'Should retrieve the computer info' {
-                        Assert-MockCalled -CommandName 'Get-ComputerInfo' -Exactly 1 -Scope 'Context'
-                    }
-
-                    It 'Should return true' {
-                        Test-IsNanoServer | Should -Be $true
-                    }
+            Context 'Computer OS type is Server and OS server level is NanoServer' {
+                Mock -CommandName 'Test-Path' -MockWith { return $true }
+                Mock -CommandName 'Get-ItemProperty' -MockWith { return $testComputerInfoNanoServer }
+                It 'Should not throw' {
+                    { $null = Test-IsNanoServer } | Should -Not -Throw
                 }
 
-                Context 'Computer OS type is Server and OS server level is not NanoServer' {
-                    Mock -CommandName 'Get-ComputerInfo' -MockWith { return $testComputerInfoServerNotNano }
-
-                    It 'Should not throw' {
-                        { $null = Test-IsNanoServer } | Should -Not -Throw
-                    }
-
-                    It 'Should test if the Get-ComputerInfo command exists' {
-                        $testCommandExistsParameterFilter = {
-                            return $Name -eq 'Get-ComputerInfo'
-                        }
-
-                        Assert-MockCalled -CommandName 'Test-CommandExists' -ParameterFilter $testCommandExistsParameterFilter -Exactly 1 -Scope 'Context'
-                    }
-
-                    It 'Should retrieve the computer info' {
-                        Assert-MockCalled -CommandName 'Get-ComputerInfo' -Exactly 1 -Scope 'Context'
-                    }
-
-                    It 'Should return false' {
-                        Test-IsNanoServer | Should -Be $false
-                    }
+                It 'Should check the ServerLevels registry path' {
+                    Assert-MockCalled -CommandName 'Get-ItemProperty' -Exactly 1 -Scope 'Context'
                 }
 
-                Context 'Computer OS type is not Server' {
-                    Mock -CommandName 'Get-ComputerInfo' -MockWith { return $testComputerInfoNotServer }
-
-                    It 'Should not throw' {
-                        { $null = Test-IsNanoServer } | Should -Not -Throw
-                    }
-
-                    It 'Should test if the Get-ComputerInfo command exists' {
-                        $testCommandExistsParameterFilter = {
-                            return $Name -eq 'Get-ComputerInfo'
-                        }
-
-                        Assert-MockCalled -CommandName 'Test-CommandExists' -ParameterFilter $testCommandExistsParameterFilter -Exactly 1 -Scope 'Context'
-                    }
-
-                    It 'Should retrieve the computer info' {
-                        Assert-MockCalled -CommandName 'Get-ComputerInfo' -Exactly 1 -Scope 'Context'
-                    }
-
-                    It 'Should return false' {
-                        Test-IsNanoServer | Should -Be $false
-                    }
+                It 'Should return true' {
+                    Test-IsNanoServer | Should -Be $true
                 }
             }
 
-            Context 'Get-ComputerInfo command exists but throws an error and returns null' {
-                Mock -CommandName 'Get-ComputerInfo' -MockWith { return $null }
+            Context 'Computer OS type is Server and OS server level is not NanoServer' {
+                Mock -CommandName 'Test-Path' -MockWith { return $true }
+                Mock -CommandName 'Get-ItemProperty' -MockWith { return $testComputerInfoServerNotNano }
 
                 It 'Should not throw' {
                     { $null = Test-IsNanoServer } | Should -Not -Throw
                 }
 
-                It 'Should test if the Get-ComputerInfo command exists' {
-                    $testCommandExistsParameterFilter = {
-                        return $Name -eq 'Get-ComputerInfo'
-                    }
-
-                    Assert-MockCalled -CommandName 'Test-CommandExists' -ParameterFilter $testCommandExistsParameterFilter -Exactly 1 -Scope 'Context'
-                }
-
-                It 'Should retrieve the computer info' {
-                    Assert-MockCalled -CommandName 'Get-ComputerInfo' -Exactly 1 -Scope 'Context'
+                It 'Should check the ServerLevels registry path' {
+                    Assert-MockCalled -CommandName 'Get-ItemProperty' -Exactly 1 -Scope 'Context'
                 }
 
                 It 'Should return false' {
                     Test-IsNanoServer | Should -Be $false
                 }
             }
 
-            Context 'Get-ComputerInfo command does not exist' {
-                Mock -CommandName 'Test-CommandExists' -MockWith { return $false }
+            Context 'Computer OS type is not Server' {
+                Mock -CommandName 'Test-Path' -MockWith { return $false }
 
                 It 'Should not throw' {
                     { $null = Test-IsNanoServer } | Should -Not -Throw
                 }
 
-                It 'Should test if the Get-ComputerInfo command exists' {
-                    $testCommandExistsParameterFilter = {
-                        return $Name -eq 'Get-ComputerInfo'
-                    }
-
-                    Assert-MockCalled -CommandName 'Test-CommandExists' -ParameterFilter $testCommandExistsParameterFilter -Exactly 1 -Scope 'Context'
-                }
-
-                It 'Should not attempt to retrieve the computer info' {
-                    Assert-MockCalled -CommandName 'Get-ComputerInfo' -Exactly 0 -Scope 'Context'
+                It 'Should check the ServerLevels registry path' {
+                    Assert-MockCalled -CommandName 'Test-Path' -Exactly 1 -Scope 'Context'
                 }
 
                 It 'Should return false' {