Vector Config Unit Testing Improvements

Support for unit testing transforms with multiple outputs

We’ve added support for unit testing transforms with multiple outputs as well as full support for testing task-style transforms (previously there may have been issues when using multiple inputs with task transforms). For example, you can now test remap transform’s dropped output like so,

  type = "remap"
  inputs = []
  drop_on_abort = true
  reroute_dropped = true
  source = "abort"

  name = "remap_dropped_output"
  no_outputs_from = [ "foo" ]

    insert_at = "foo"
    type = "log"
      message = "I will be dropped"

    extract_from = "foo.dropped"

      type = "vrl"
      source = 'assert_eq!(.message, "I will be dropped", "incorrect message")'

Under-the-hood, we’ve reworked the unit testing implementation to more closely align with how a configuration actually runs, making it easier to support testing new features. However, as a result, some unit testing debug UX has also changed: previously, on a test condition error, debug output included input event information representing the event(s) prior to being transformed. input event information is no longer available. The original input event(s) for a test can be determined from your configuration.