What is the best strategy for testing D3/HighCharts/SVG?

Question

Our server generates the data and then the client generates charts using HighCharts which is SVG. We are struggling to write an automated test in order to verify that the generated chart is correct.

This is what the SVG HighCharts generates

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142.5 321" stroke="#C0D0E0" stroke-width="1" opacity="1"></path><path fill="none" d="M 181.5 316 L 181.5 321" stroke="#C0D0E0" stroke-width="1" opacity="1"></path><path fill="none" d="M 219.5 316 L
219.5 321" stroke="#C0D0E0" stroke-width="1" opacity="1"></path><path fill="none" d="M 258.5 316 L 258.5 321" stroke="#C0D0E0" stroke-width="1" opacity="1"></path><path fill="none" d="M 297.5 316 L
297.5 321" stroke="#C0D0E0" stroke-width="1" opacity="1"></path><path fill="none" d="M 336.5 316 L 336.5 321" stroke="#C0D0E0" stroke-width="1" opacity="1"></path><path fill="none" d="M 103.5 316 L
103.5 321" stroke="#C0D0E0" stroke-width="1" opacity="1"></path><path fill="none" d="M 65.5 316 L 65.5 321" stroke="#C0D0E0" stroke-width="1"></path><text x="201" y="373" style="font-family:Tahoma, Arial, sans-serif;font-size:9pt;color:#505050;font-weight:bold;fill:#505050;" zIndex="7" text-anchor="middle" transform="translate(0,0)" visibility="visible"><tspan x="201">Project</tspan></text><path fill="none" d="M 65 315.5 L 337 315.5" stroke="#505050" stroke-width="1" zIndex="7" visibility="visible"></path></g><g class="highcharts-axis" zIndex="2"><text x="24.9375" y="178" style="font-family:Tahoma, Arial, sans-serif;font-size:9pt;color:#505050;font-weight:bold;fill:#505050;" zIndex="7" text-anchor="middle" transform="translate(0,0) rotate(270
24.9375 178)" visibility="visible"><tspan x="24.9375">Percent Complete (%)</tspan></text></g><g class="highcharts-series-group" zIndex="3"><g class="highcharts-series highcharts-tracker highcharts-tracker highcharts-tracker highcharts-tracker" visibility="visible" zIndex="0.1" transform="translate(65,40) scale(1 1)" style="" clip-path="url(#highcharts-1)"><rect fill="#9F2727" x="3.5" y="275.5" width="31" height="0" stroke="#FFFFFF" stroke-width="1" rx="0" ry="0"></rect><rect fill="#9F2727" x="42.5" y="275.5" width="31" height="0" stroke="#FFFFFF" stroke-width="1" rx="0" ry="0"></rect><rect fill="#9F2727" x="81.5" y="59.5" width="31" height="216" stroke="#FFFFFF" stroke-width="1" rx="0" ry="0"></rect><rect fill="#9F2727" x="120.5" y="144.5" width="31" height="131" stroke="#FFFFFF" stroke-width="1" rx="0" ry="0"></rect><rect fill="#9F2727" x="159.5" y="13.5" width="31" height="262" stroke="#FFFFFF" stroke-width="1" rx="0" ry="0"></rect><rect fill="#9F2727" x="198.5" y="236.5" width="31" 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style="font-family:&quot;HelveticaNeue-Roman&quot;, &quot;HelveticaNeue&quot;, &quot;Helvetica Neue&quot;, &quot;Helvetica&quot;, &quot;Arial&quot;, sans-serif;font-size:11px;color:#000000;line-height:14px;fill:#000000;" zIndex="1"></text></g><g zIndex="1" style="cursor:default;" transform="translate(82,40)" visibility="inherit"><text x="3" y="15" style="font-family:&quot;HelveticaNeue-Roman&quot;, &quot;HelveticaNeue&quot;, &quot;Helvetica Neue&quot;, &quot;Helvetica&quot;, &quot;Arial&quot;, sans-serif;font-size:11px;color:#000000;line-height:14px;fill:#000000;" zIndex="1"><tspan x="3">41%</tspan></text></g><g zIndex="1" style="cursor:default;" transform="translate(121,125)" visibility="inherit"><text x="3" y="15" style="font-family:&quot;HelveticaNeue-Roman&quot;, &quot;HelveticaNeue&quot;, &quot;Helvetica Neue&quot;, &quot;Helvetica&quot;, &quot;Arial&quot;, sans-serif;font-size:11px;color:#000000;line-height:14px;fill:#000000;" zIndex="1"><tspan x="3">25%</tspan></text></g><g zIndex="1" style="cursor:default;" transform="translate(160,-6)" visibility="inherit"><text x="3" y="15" style="font-family:&quot;HelveticaNeue-Roman&quot;, &quot;HelveticaNeue&quot;, &quot;Helvetica Neue&quot;, &quot;Helvetica&quot;, &quot;Arial&quot;, sans-serif;font-size:11px;color:#000000;line-height:14px;fill:#000000;" zIndex="1"><tspan x="3">50%</tspan></text></g><g zIndex="1" style="cursor:default;" transform="translate(202,217)" visibility="inherit"><text x="3" y="15" style="font-family:&quot;HelveticaNeue-Roman&quot;, &quot;HelveticaNeue&quot;, &quot;Helvetica Neue&quot;, &quot;Helvetica&quot;, &quot;Arial&quot;, sans-serif;font-size:11px;color:#000000;line-height:14px;fill:#000000;" zIndex="1"><tspan x="3">8%</tspan></text></g><g zIndex="1" style="cursor:default;" transform="translate(238,53)" visibility="inherit"><text x="3" y="15" style="font-family:&quot;HelveticaNeue-Roman&quot;, &quot;HelveticaNeue&quot;, &quot;Helvetica Neue&quot;, &quot;Helvetica&quot;, &quot;Arial&quot;, sans-serif;font-size:11px;color:#000000;line-height:14px;fill:#000000;" zIndex="1"><tspan x="3">39%</tspan></text></g></g><g class="highcharts-legend" zIndex="7" transform="translate(94,404)"><rect rx="5" ry="5" fill="#FFFFFF" x="0" y="0" width="158" height="31" visibility="visible"></rect><g zIndex="1"><g><g class="highcharts-legend-item" zIndex="1" transform="translate(8,3)"><text x="21" y="15" style="font-family:Tahoma, Arial, sans-serif;font-size:9pt;cursor:pointer;color:#274b6d;fill:#274b6d;" text-anchor="start" zIndex="2"><tspan x="21">Percent Complete-Sum</tspan></text><rect rx="2" ry="2" fill="#9F2727" x="0" y="4" width="16" height="12" zIndex="3"></rect></g></g></g></g><g class="highcharts-axis-labels" zIndex="7"></g><g class="highcharts-axis-labels" zIndex="7"><text x="57" y="322.3421875" style="font-family:Tahoma, Arial, sans-serif;font-size:8pt;width:116px;color:#666;cursor:default;line-height:14px;fill:#666;" text-anchor="end" opacity="1"><tspan x="57">0</tspan></text><text x="57" y="217.19933035714288" style="font-family:Tahoma, Arial, sans-serif;font-size:8pt;width:116px;color:#666;cursor:default;line-height:14px;fill:#666;" text-anchor="end" opacity="1"><tspan x="57">20%</tspan></text><text x="57" y="112.05647321428572" style="font-family:Tahoma, Arial, sans-serif;font-size:8pt;width:116px;color:#666;cursor:default;line-height:14px;fill:#666;" text-anchor="end" opacity="1"><tspan x="57">40%</tspan></text></g><g class="highcharts-tooltip" zIndex="8" style="cursor:default;padding:0;white-space:nowrap;" visibility="hidden" transform="translate(46,45)" opacity="0"><rect rx="3" ry="3" fill="none" x="0.5" y="0.5" width="182" height="31" fill-opacity="0.85" isShadow="true" stroke="black" stroke-opacity="0.049999999999999996" stroke-width="5" transform="translate(1, 1)"></rect><rect rx="3" ry="3" fill="none" x="0.5" y="0.5" width="182" height="31" fill-opacity="0.85" isShadow="true" stroke="black" 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Our current strategy is to generate the SVG baselines in all browsers, save them, rerun the SVG generation using selenium driver and compare the two XML response naively.

However we noticed that the DPI and the browser heavily affects height and width of the svg, which makes the tests brittle. We also tried taking screenshots of the two charts and comparing however it was very resolution dependent.

Currently we complement the UI tests with unit tests that makes sures the input to highcharts is correct, but we want to make sure we cover all the bases.

Please help us determine the correct strategy to test SVG elements generated by libraries like highcharts and d3.js.

Thank you very much.

Answer 1

I think you're on the right path, using Selenium to verify the dimensions of the various elements of the chart. The key is to verify their relative dimensions compared to the <svg>'s size, maybe allowing a small margin of error, and not their absolute ones.