Provide a message with expect

[flwyd]

Is your feature request related to a problem?

The error message for a failing expect call doesn't provide a lot of context about which line is failing. For example, # Expected 2 to equal '1' if there are several expect calls in the test, all of which involve numbers, or perhaps when checking a property of a list of items in a loop.

Describe the solution you'd like

I'd like to specify a message as part of the expect chain, much as one can be provided with assert calls. I can think of a couple ways this could be done:

• Optional parameter: s:expect(len(l:mylist), 'should have one element').to_equal(1)
• Chained function calls: s:expect(len(l:mylist)).with_message('should have one element').to_equal(1)
• Provide message as a context:

  let s:withmsg = themis#helper('with_message')
  call s:withmsg('should have one element').expect(len(l:mylist)).to_equal(1)
  " could wrap assert, too
  call s:withmsg('should be upper case').assert.match(l:mylist[0], '^[A-Z]\+l')

[thinca]

expect-helper was added by @cohama. @cohama, what do you think?

FYI, helper functions from assert-helper can accept {message} argument.

[cohama]

I prefer 'chained function calls'.

I will try to implement it.