When Montresor says he was so glad to see Fortunato that “I thought I should never have done wringing his hand”, Poe is using irony.
Explanation:
In "The cask of amontillado" by Edgar Allan Poe, the line “I thought I should never have done wringing his hand” is an example of irony since Montresor had always said Fortunato was his enemy and has even thought and planned his revenge against him, then at this moment he is being ironic by saying something opposite to his real intentions.