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Is there a keyword in Robot Framework to ensure element has a certain class? Something like

Element should has class element className

Alternatively, I could check if element has a certain attribute with certain value. Former would be more suitable though, as element may contain multiple classes.

Answers

You could create a new keyword via XPath selectors:

Element should have class
    [Arguments]  ${element}  ${className}
    Wait until page contains element  ${element}[contains(@class, '${className}')]

Or via CSS selectors:

Element should have class
    [Arguments]  ${element}  ${className}
    Wait until page contains element  ${element}.${className}

Wait until page contains element could be replaced by any keyword of your liking to check if the element exists and is visible, such as Element should be visible.