Open a tab of the product page by its name ("Details", "More Information", "Reviews"; the review counter after the name is not part of it). The reviews are fetched when their tab is opened for the first time: the step waits for them.
Examples
When I open the "Reviews" product tab
When I open the "Details" product tab
And I open the "More Information" product tab
When we open the "Reviews" product tab
When open the "Details" product tab
Pattern
When(/^(I |we )*open the "([^"]*)" product tab$/, …)
Part of @webship-js/magento-steps (github.com/webship/magento-steps), a step pack for Webship-js 2.0.x.