Add integration tests for fetch/slurp, make powershell fetch/slurp work as close as possible to existing fetch/slurp modules.

windows/slurp.ps1

@@ -33,15 +33,32 @@ Else
 }
 If (-not $src)
 {
-
+    $result = New-Object psobject @{};
+    Fail-Json $result "missing required argument: src";
 }
 
-$bytes = [System.IO.File]::ReadAllBytes($src);
-$content = [System.Convert]::ToBase64String($bytes);
+If (Test-Path $src)
+{
+    If ((Get-Item $src).Directory) # Only files have the .Directory attribute.
+    {
+        $bytes = [System.IO.File]::ReadAllBytes($src);
+        $content = [System.Convert]::ToBase64String($bytes);
 
-$result = New-Object psobject @{
+        $result = New-Object psobject @{
             changed = $false
             encoding = "base64"
-};
-Set-Attr $result "content" $content;
-Exit-Json $result;
+        };
+        Set-Attr $result "content" $content;
+        Exit-Json $result;
+    }
+    Else
+    {
+        $result = New-Object psobject @{};
+        Fail-Json $result ("is a directory: " + $src);
+    }
+}
+Else
+{
+    $result = New-Object psobject @{};
+    Fail-Json $result ("file not found: " + $src);
+}