How to add .txt file to firebase storage when cloud function is triggered?

Question

I have a cloud function which checks if update field is true in {user} document field.

I have text file in my functions folder, path: functions/test.txt

When the update becomes true, a new collection is created with description "update triggered". How do I upload my test.txt file to firebase storage only when the update:true is triggered?

exports.statusUpdate = functions.firestore.document("test/{user}")
.onUpdate((change, context) => {
     let user = context.params.user
     const newValue = change.after.data();
     const previousValue = change.before.data();
   if(newValue.update == true) {
      db.collection('true').add({description: `update triggered`})
      //upload the test.txt file in firebase storage
 }  })