foo.rb

# For @echorand :)

require 'test/unit'

class Float
  class NoYouCantBecauseMaths < RuntimeError; end

  def even?
    raise NoYouCantBecauseMaths unless whole_number?
    to_i.even?
  end

  def odd?
    raise NoYouCantBecauseMaths unless whole_number?
    to_i.odd?
  end

  private

  def whole_number?
    self == to_i
  end
end

class FloatEvenOddTest < Test::Unit::TestCase
  def test_the_madness
    assert !10.odd?
    assert 10.even?

    assert 11.odd?
    assert !11.even?

    assert !10.0.odd?
    assert 10.0.even?

    assert !11.0.even?
    assert 11.0.odd?

    assert !1.234.send(:whole_number?)
    assert !1.001.send(:whole_number?)
    assert 1.000.send(:whole_number?)

    assert_raise(Float::NoYouCantBecauseMaths) { 6.50.even? }
    assert_raise(Float::NoYouCantBecauseMaths) { 6.50.odd? }
  end
end

output.txt

Loaded suite foo
Started
.
Finished in 0.000342 seconds.

1 tests, 13 assertions, 0 failures, 0 errors