Add test site procedure

Author: maxvp

src/content/docs/cloudflare-one/policies/gateway/http-policies/file-sandboxing.mdx

@@ -55,6 +55,24 @@ To begin quarantining downloaded files, turn on file sandboxing:
 
 You can now create [Quarantine HTTP policies](/cloudflare-one/policies/gateway/http-policies/#quarantine) to determine what files to scan in the sandbox.
 
+## Test file sandboxing
+
+To test file sandboxing, you can create a Quarantine policy that matches the [Cloudflare Sandbox Test](https://sandbox.cloudflaredemos.com/):
+
+1. In [Zero Trust](https://one.dash.cloudflare.com/), go to **Gateway** > **Firewall policies**, then select **HTTP**.
+2. Select **Add a policy**.
+3. Add the following expression:
+
+   | Selector | Operator | Value                         | Action     |
+   | -------- | -------- | ----------------------------- | ---------- |
+   | Host     | is       | `sandbox.cloudflaredemos.com` | Quarantine |
+
+4. In **Sandbox file types**, select _ZIP Archive (zip)_.
+5. From a device [connected to your Zero Trust organization](/cloudflare-one/connections/connect-devices/), open a browser and go to the [Cloudflare Sandbox Test](https://sandbox.cloudflaredemos.com/).
+6. Select **Download Test File**.
+
+Before downloading the test file to the device, Gateway will quarantine and scan the file while displaying an interstitial status page.
+
 ## Compatibility
 
 ### Supported file types