expect_message() could be more helpful if expected string is not matched

[mcol]

This got me stuck for a while:

expect_message(cli::cli_alert_warning("'args' contains only fixed elements"),
               "'args' contans only fixed elements")

# ! 'args' contains only fixed elements
# Error: Expected `cli::cli_alert_warning("'args' contains only fixed elements")` to throw a message.

Initially I thought that perhaps for cli_alert_warning() I should have used expect_output() or expect_warning(), but neither of those helped. Only after a lot of head-scratching I realised that there was a typo in my expectation.

I think the wording expected to throw a message is misleading when a message is actually being thrown. Ideally in such case, it should say something like:

  `actual`: ! 'args' contains only fixed elements
`expected`: ! 'args' contans only fixed elements