Nifty Proxy Object for Testing

Discussion in 'Ruby' started by Brian Schröder, Oct 17, 2005.

  1. Hello Group,

    I had an idea for a testing method I wanted to share. I develop a c
    extension that efficently implements a priority queue. An inefficent
    pure ruby reference implementation can easily be written, so I have a
    reference implementation and my c implementation and want to assure
    that they behave the same. I achieve this by using a proxy object in
    my tests that does all actions on both implementations and asserts
    that return values and thrown exceptions are equal.

    That allows for double testing. I assure that my normal unit tests
    work and additionally for each action it is tested that the right
    thing is returned. Furthermore the teardown method now tests that the
    actions have resulted in the same state in both implementations.

    Ideas, thoughts, critcal voices?


    See below for the implementation and usage

    class ReferenceImplementationTester
    attr_reader :__implementations__

    def initialize(testcase, reference, implementation)
    @testcase =3D testcase
    @reference =3D reference
    @implementation =3D implementation
    @__implementations__ =3D {:reference =3D> @reference, :implementation
    =3D> @implementation}

    def method_missing(method, *args, &block)
    method_description =3D "#{method}(#{args.join(', ')})"
    method_description << " do <##{block.object_id} ...> end" if block_give=

    r1 =3D begin
    =09 @reference.send(method, *args, &block)
    =09 rescue Object =3D> e1
    =09 end
    r2 =3D begin
    =09 @implementation.send(method, *args, &block)
    =09 rescue Object =3D> e2
    =09 end
    r1 =3D :___SELF_RETURNED___ if (r1 =3D=3D @reference)
    r2 =3D :___SELF_RETURNED___ if (r2 =3D=3D @implementation)
    @testcase.assert_equal(e1, e2,
    =09=09 "#{method_description} raised different exceptions on
    #{@reference.inspect} and on #{@implementation.inspect}")
    @testcase.assert_equal(r1, r2,
    =09=09 "#{method_description} returned different results on
    #{@reference.inspect} and on #{@implementation.inspect}")

    class PriorityQueueReferenceTester < ReferenceImplementationTester
    def initialize(testcase)

    class PriorityQueueTest < Test::Unit::TestCase
    # Create a new queue with automatic tests against the reference implement=
    def setup
    @q =3D

    # Test that both implementations return the same elements on delete min
    def teardown
    true while @q.delete_min

    # Assure that delete_min works
    def test_delete_min
    assert_equal(nil, @q.delete_min, "Empty queue should pop nil")
    @q["n1"] =3D 0
    assert_equal(["n1", 0], @q.delete_min)
    @q["n1"] =3D 0
    @q["n2"] =3D -1
    assert_equal(["n2", -1], @q.delete_min)

    # Try on random values
    def test_random_actions
    100.times do
    @q[rand(10)] =3D rand
    15.times do
    Brian Schröder, Oct 17, 2005
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  2. Maybe I didn't understand this correctly but if you have "normal" unit
    tests already, why then do you need a result comparison? I mean, if
    instances of both classes pass the unit test results should be the same or
    at least compatible.

    Alternatively you could use the Ruby implementation to yield expected
    values that are compared with the C version, but that has the same problem
    as a comparison only test: you won't catch algorithmic flaws that you made
    (if you developed both it's likely that both exhibit the same erroneous
    behavior which you won't catch with the comparison approach).

    Kind regards

    Robert Klemme, Oct 17, 2005
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  3. Hello robert,

    my idea was that it is a lot easier to write a functional (bugfree)
    ruby version. Of course it would be possible to write good unit test
    and use them on both implementations, but I hope to get better
    coverage using this approach as I'm checking the result of each and
    every action. But beware, I'm relatively inexperienced in writing good
    unit tests, so maybe the whole idea does not make much sense.

    best regards,

    Brian Schröder, Oct 17, 2005
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