Update Get-AADGroupByDisplayName Unit Test

* Goal reached for markekraus/PSMSGraph#8
* Added missing code coverage for ```Invoke-GrapRequest``` error handling
* Now has 100% code coverage for ```Get-AADGroupByDisplayName```

Author: markekraus

Tests/Get-AADGroupByDisplayName.Unit.Tests.ps1

@@ -70,11 +70,18 @@ $VerifyUrl = @(
      '/groups'
      '?api-version=1.6'
      '&$filter=displayName+eq+%27Marketing%27'
-     
+) -Join ''
+$VerifyBadUrl = @(
+     'https://graph.windows.net/'
+     $AppParams.Tenant
+     '/groups'
+     '?api-version=1.6'
+     '&$filter=displayName+eq+%27BadGroup%27'
 ) -Join ''
 
 $ValidUrls = @(
     $VerifyUrl
+    $VerifyBadUrl
 )
 # https://msdn.microsoft.com/en-us/library/azure/ad/graph/api/groups-operations
 $Global:AADGroupJSON = @'
@@ -110,6 +117,9 @@ Describe $Command -Tags Unit {
         }
         return $MockResponse
     }
+    Mock -CommandName Invoke-GraphRequest -ModuleName PSMSGraph -ParameterFilter {$Uri -eq $ValidUrls[1]} -MockWith {
+        Throw 'invalid group'
+    }
     It 'Does not have errors when passed required parameters' {
         $LocalParams = $Params.psobject.Copy()
         { & $Command @LocalParams -ErrorAction Stop } | Should not throw
@@ -134,6 +144,11 @@ Describe $Command -Tags Unit {
         $Object = & $Command @LocalParams | Select-Object -First 1
         $Object._AccessToken.GUID | should be $Token.GUID
     }
+    It 'Provides friendly errors' {
+         $LocalParams = $Params.psobject.Copy()
+         $LocalParams.DisplayName = 'BadGroup'
+        { & $Command @LocalParams -ErrorAction Stop } | Should not throw 'Unable to query Group'
+    }
 }
 
 Remove-Variable -Name 'AADGroupJSON' -Scope 'Global'