The option to download the digital version should only appear in the books that support this feature.
User interface mockups
Acceptance tests
Scenario: Download Digital Version
Given I have navigated to the details page of a specific book
And that book has an available digital version
When I tap the "E-book" button
Then I should have access to its digital version
Scenario: Digital Version Unavailable
Given I have navigated to the details page of a specific book
And that book does not have a digital version
Then I should not see an "E-book" button
Notes
The option to download the digital version should only appear in the books that support this feature.
User interface mockups
Acceptance tests
Value and effort