Updated Get-MyAWSRegion with robust code and tests

Functions/Get-MyAWSRegion.Tests.ps1

@@ -1,13 +1,33 @@
-$here = Split-Path -Parent $MyInvocation.MyCommand.Path
-$sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path).Replace(".Tests.", ".")
-. "$here\$sut"
+#requires -Version 3 -Modules AWSPowerShell
+
+$currentDirectory = Split-Path -Parent $PSCommandPath
+$sourceFile = (Split-Path -Leaf $PSCommandPath).Replace(".Tests.", ".")
+. "$currentDirectory\$sourceFile"
 
 Describe "Get-MyAWSRegion" {
-	Mock Invoke-RestMethod { return 'regionA' }
 
-	$result = Get-MyAWSRegion
+    It "An internal error should throw an exception" {
+
+        Mock -CommandName Invoke-RestMethod -MockWith {throw}
+
+        { Get-MyAWSRegion } | Should throw
+	}
+
+    It "With mock checking for null" {
+
+        Mock -CommandName Invoke-RestMethod -MockWith {$null}
+
+        {Get-MyAWSRegion} | Should throw
+	}
+
+	It "With mock checking return value" {
+
+        $mockObject = New-Object PSCustomObject
+        $mockObject | Add-Member -MemberType NoteProperty �Name "region" �Value "regionA"
+        $actualOutput = "regionA"
+
+        Mock -CommandName Invoke-RestMethod -MockWith {$mockObject}
 
-	It "returns region" {
-		$result | Should be 'region'
+        Get-MyAWSRegion | Should Be $actualOutput
 	}
 }

Functions/Get-MyAWSRegion.ps1

@@ -1,9 +1,20 @@
 <#
-    .Synopsis
-    When run on an EC2 instance it will return the region that the instance is in
+.Synopsis
+   When run on an EC2 instance it will return the region that the instance is in
+.OUTPUTS
+   Region name in string
+.EXAMPLE
+   Get-MyAWSRegion 
 #>
-
-function Get-MyAWSRegion {
-	$availability_zone = Invoke-RestMethod 'http://169.254.169.254/latest/meta-data/placement/availability-zone'
-    return $availability_zone.Substring(0, $availability_zone.Length - 1)
+function Get-MyAWSRegion 
+{
+    [OutputType([String])]
+
+    $metadata = Invoke-RestMethod 'http://169.254.169.254/latest/dynamic/instance-identity/document'
+    if (!$metadata)
+    {
+        throw "Metadata information could not be retrieved"
+    }
+    return $metadata.region
 }
+