How about

  class Epsilon
    @epsilon
    def initialize( epsilon )
      @epsilon = epsilon
    end
    def test(actual, excepted)
      return (a-b).abs < @epsilon
    end
  end

  class DigitPrecision < Epsilon
    def initialize( digitCount )
      @epsilon = 0.1 ** (digitCount)
    end
  end

  def assert_equal_float(actual, expected, tester = Epsilon.new(0.00001))
    tester.test(actual, expected)
    ...
  end

  assert_equal_float(Math.sqrt(2), 1.414, Epsilon.new(0.001))
  assert_equal_float(Math.sqrt(2), 1.414, DigitPrecision(3))

> Probably I can code the X digit checking version, but I have no 
> good name of the method. Do you have any good idea about the 
> name of the method with X digit checking versi

But DigitPrecision is bad name IMHO, and I didn't even dare to answer to
your question :(.

	- Aleksi