Search for a term by filling the keyword field (input[name="keys"], the name core uses for both the search block and the search page) and submitting.
Examples
When I search for "webship"
And we search for "cucumber"
When search for "playwright"
And I search for "sample title"
When we search for "example"
Pattern
When(/^(I |we )*search for "([^"]*)?"$/, …)
Part of @webship-js/drupal-core-steps (github.com/webship/drupal-core-steps), a step pack for Webship-js 2.0.x.