test: make convertToTspans suite more robust
test: make convertToTspans suite more robust

- check for white list of anchor attributes
- check for correct 'xlink:show' value

asolagmbh/plotly.js,aburato/plotly.js,iongroup/plotly.js,iongroup/plotly.js,etpinard/plotly.js,iongroup/plotly.js,plotly/plotly.js,plotly/plotly.js,plotly/plotly.js,plotly/plotly.js,asolagmbh/plotly.js,etpinard/plotly.js,aburato/plotly.js,asolagmbh/plotly.js,etpinard/plotly.js