If you are writing a rule that runs an action that takes an array parameter, you need to use JSON-style notation for your array.
So your rule should look something like this:
---
name: "myrule"
pack: "default"
description: "example rule to trigger action taking an array"
enabled: true
trigger:
type: "my.trigger"
criteria:
trigger.body:
type: "iequals"
pattern: "testing"
action:
ref: "default.myaction"
parameters:
ArrayParameter: ["foo", "bar"]