(Julia 0.5 only) Concept still good, but needs updating for julia 1.0



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Julia has several "Informal Interfaces". Unlike many mainstream static languages, interfaces are not statically defined. Nor, can it be directly required that concrete types of an abstract type implement certain methods.

The Iterator interface is very common. It is also very easy to mess up. Eg by forgetting to define iteratorsize, or by defining it on the values, rather than on the types.

This package makes testing it simple.

If in your src file you have defined an iterator SomeRandomNumbers

module CountingGames
    export SomeRandomNumbers
    immutable SomeRandomNumbers end
    Base.start(::SomeRandomNumbers) = 1
    Base.done(::SomeRandomNumbers, state) = state>100
    Base.iteratorsize(::Type{SomeRandomNumbers}) = Base.SizeUnknown()
    function Base.next(::SomeRandomNumbers, state)
        ret = rand(1:10)
        ret, state+ret

then you can check it meets all the requirements by writing a tests:

using Base.Test
using CountingGames
using InterfaceTesting


This will run a @testset to check everything is defined correctly:

Test Summary:                   | Pass  Total
  CountingGames.SomeRandomNumbers |    5      5

On testing parametric types

If your type takes a parameter, eg Foo{T}, you are better to run the tests with that parameter filled in. Eg test_iterator_interface(Foo{Int}) rather than test_iterator_interface(Foo). Because of how dispatch to parametric types works. Foo{T} != Foo but Foo{T} <: Foo. This means that if you have defined iteratorsize{T}{::Type{Foo{T}}) generally the test_iterator_interface(Foo) will fail as that definion does not apply to Foo. It is complicated like that. But the take away should be to fill in your type parameters when using these tests.

Supported Interfaces

The focus of this package is the testing of the Iterator interface, with its several traits and complexities. it does support several others, though these have not had as much testing or thought put in.

First Commit


Last Touched

8 months ago


11 commits


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