Add simple securestring conversion cmdlet tests

test/powershell/Modules/Microsoft.PowerShell.Security/SecureString.Tests.ps1

@@ -0,0 +1,45 @@
+Describe "SecureString conversion tests" -Tags "CI" {
+    BeforeAll {
+        $string = "ABCD"
+        $secureString = [System.Security.SecureString]::New()
+        $string.ToCharArray() | foreach-object { $securestring.AppendChar($_) }
+        $defaultParamValues = $PSdefaultParameterValues.Clone()
+        $PSdefaultParameterValues = @{}
+        if ( ! $IsWindows ) { $PSdefaultParameterValues["it:pending"] = $true }
+    }
+    AfterAll {
+        $PSdefaultParameterValues = $defaultParamValues 
+    }
+
+    It "using null arguments to ConvertFrom-SecureString produces an exception" {
+        try {
+            ConvertFrom-SecureString -secureString $null -key $null
+        }
+        catch {
+            $_.FullyQualifiedErrorId | should be "ParameterArgumentValidationErrorNullNotAllowed,Microsoft.PowerShell.Commands.ConvertFromSecureStringCommand"
+        }
+        
+    }
+    
+    It "using a bad key produces an exception" {
+        try {
+            $badkey = [byte[]]@(1,2)
+            ConvertFrom-SecureString -securestring $secureString -key $badkey
+            throw "Execution OK"
+        }
+        catch {
+            $_.FullyQualifiedErrorId | should be "Argument,Microsoft.PowerShell.Commands.ConvertFromSecureStringCommand"
+        }
+    }
+
+    It "Can convert to a secure string" {
+        $ss = ConvertTo-SecureString -AsPlainText -Force abcd
+        $ss.GetType().Name | should be "SecureString"
+    }
+    It "can convert back from a secure string" {
+        $secret = "abcd"
+        $ss1 = ConvertTo-SecureString -AsPlainText -Force $secret
+        $ss2 = convertfrom-securestring $ss1 | convertto-securestring
+        [pscredential]::New("user",$ss2).GetNetworkCredential().Password | should be $secret
+    }
+}