Guidance for using Percy and dash.testing correctly, styles and webgl do not seem to work?


I’m trying out the new dash.testing functionality with Percy.

Local screenshots seem to be fine, but the snapshots uploaded to Percy do not have CSS styles and also WebGL content does not appear. Is this correct, or am I doing something wrong?

Thanks for any guidance!


For additional context, the CSS styles are displaying correctly in the Chrome WebDriver I’m using during testing. I can understand that Percy might not display WebGL content, but I’m surprised the styles aren’t working.

CSS - we just hit this exact issue ourselves in upgrading dash docs to use dash.testing. @byronz can give more details, but the issue is pointing Percy at the right assets folder. We added an option --percy-assets for this in but it hasn’t been released yet - you either need to wait for dash 1.3 (due out this week) or you need the dev branch of dash from github.

WebGL - Percy can’t access anything in a <canvas> - in our own tests we don’t worry about this, but here’s someone who found a workaround:

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Thanks @alexcjohnson – this is super helpful!


besides what alex mentioned, there is actually another option to configure percy’s runner behavior --nopercyfinalize. it’s needed if you run your tests in parallelism and terminate the percy with percy finalize --all

I should add a section explaining the details in the dash-docs

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