ILinePlot: test independent series merging
ILinePlot: test independent series merging

This tests checks the following:

    - given two data series with different indexes
    - ILinePlot will merge them using _fix_indexes
    - the set of indexes of the merged series must be the union of the set of
      indexes of the initial series

sinkap/trappy,bjackman/trappy,sinkap/trappy,ARM-software/trappy,ARM-software/trappy,ARM-software/trappy,joelagnel/trappy,bjackman/trappy,ARM-software/trappy,joelagnel/trappy,sinkap/trappy,joelagnel/trappy,bjackman/trappy,bjackman/trappy,joelagnel/trappy,sinkap/trappy