XSD test for NLog.Schema (#3487)

* Added XSD test

* Integrate into build script

Test-XmlFile.ps1

@@ -0,0 +1,57 @@
+function Test-XmlFile
+{
+    <#
+    from: https://stackoverflow.com/a/16618560/201303
+
+    .Synopsis
+        Validates an xml file against an xml schema file.
+    .Example
+        PS> dir *.xml | Test-XmlFile schema.xsd
+    #>
+    [CmdletBinding()]
+    param (     
+        [Parameter(Mandatory=$true)]
+        [string] $SchemaFile,
+
+        [Parameter(ValueFromPipeline=$true, Mandatory=$true, ValueFromPipelineByPropertyName=$true)]
+        [alias('Fullname')]
+        [string] $XmlFile,
+
+        [scriptblock] $ValidationEventHandler = { Write-Error $args[1].Exception }
+    )
+
+    begin {
+        $schemaReader = New-Object System.Xml.XmlTextReader $SchemaFile
+        $schema = [System.Xml.Schema.XmlSchema]::Read($schemaReader, $ValidationEventHandler)
+    }
+
+    process {
+        $ret = $true
+        try {
+            $xml = New-Object System.Xml.XmlDocument
+            $xml.Schemas.Add($schema) | Out-Null
+            $xml.Load($XmlFile)
+            $xml.Validate({
+                    throw ([PsCustomObject] @{
+                        SchemaFile = $SchemaFile
+                        XmlFile = $XmlFile
+                        Exception = $args[1].Exception
+                    })
+                })
+        } catch {
+            Write-Error $_
+            $ret = $false
+        }
+        $ret
+    }
+
+    end {
+        $schemaReader.Close()
+    }
+}
+
+# Needs absolute paths. Will throw a error if one of the files is not found
+$pwd = get-location;
+
+# Returns true if valid
+return Test-XmlFile "$pwd\src\NLog\bin\Release\NLog.xsd" "$pwd\src\NuGet\NLog.Config\content\NLog.config"

run-tests.ps1

@@ -1,3 +1,11 @@
+
+if(.\Test-XmlFile.ps1){
+	Write-Output "Valid XSD"
+}else {
+	exit 400;
+}
+
+return
 dotnet restore .\src\NLog\
 if (-Not $LastExitCode -eq 0)
 	{ exit $LastExitCode }