WIP: filter plugin

[edvakf]

Still working on for a better testing style.

[edvakf]

Having to convert an EventStream to an Array is unnatural. Something like this may be nicer?

    d.run do
      d.emit({'unique_id' => '1'})
      d.emit({'unique_id' => '1'}) # dup
      d.emit({'unique_id' => '2'})
      d.emit({'unique_id' => '1'})
    end

    assert_equal 3, d.output.length
    assert_equal '1', d.output[0]['unique_id']
    assert_equal '2', d.output[1]['unique_id']
    assert_equal '1', d.output[2]['unique_id']