From: Brian Candler <b.candler@...>
Date: 2010-09-01T18:07:04+09:00
Subject: Re: why no assert_not?

Martin DeMello wrote:
> Test::Unit could use a built-in antonym of assert, that succeeds if
> its argument is either false or nil.

Hmm, I would have thought "assert not ..." would work, but there is 
something odd in the parsing of 'not' as an argument:

$ ruby -v
ruby 1.8.7 (2010-01-10 patchlevel 249) [x86_64-linux]
$ irb --simple-prompt
>> not 1
=> false
>> not 3 < 4
=> false
>> puts(3 < 4)
true
=> nil
>> puts(not 3 < 4)
SyntaxError: compile error
(irb):4: syntax error, unexpected kNOT, expecting ')'
puts(not 3 < 4)
        ^
(irb):4: syntax error, unexpected ')', expecting $end
  from (irb):4
  from :0
>> puts((not 3 < 4))
false

In the past I've just done assert !(...)

But I think the issue is moot, because writing custom asserts is a 
perfectly standard thing to do. That is, just write

  def assert_not(bool, *rest)
    assert(!bool, *rest)
  end
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