VS Code: How to convert snippet placeholder from camelCase to SCREAMING_SNAKE_CASE?

I'd like to create a VS Code snippet for creating redux reducers.

I would like to have a snippet with placeholder that expects camelCase and then transform a matching placeholder to SCREAMING_SNAKE_CASE.

Here's my attempted snippet, which is not working:

"test": {
    "prefix": "test",
    "body": "${1} -> ${1/([a-zA-Z])(?=[A-Z])/${1:/upcase}_/g}"
},

Which produces a non-desired result:

changeNetworkStatus -> changE_NetworK_Status

Desired Flow

  1. type test (name of snippet)
  2. hit tab to load the snippet.
  3. type changeNetworkStatus to result in:

    changeNetworkStatus -> changeNetworkStatus
    
  4. hit tab to get expected result of:

    changeNetworkStatus -> CHANGE_NETWORK_STATUS
    

How can I change my snippet code to get the desired result?

Here's a related solution which requires a different flow.