[Bf-committers] [GSoC 2018] Questions regarding tests in Python

Howard Trickey howard.trickey at gmail.com
Fri Mar 2 16:40:43 CET 2018

On Fri, Mar 2, 2018 at 8:47 AM Łukasz Hryniuk <lukasz.hryniuk at wp.pl> wrote:

> Hi,
> I'm messing for a while with Blender sources, getting familiar with the
> code and trying to find an area I could be the most effective during the
> GSoC. I'd like to ask about the "Tests for Regressions" idea:
> 1. There are a list of areas to be tested. How they will be chosen?
> Are there any usage statistics? Further development plans? From the most
> basic ones to the most complicated? Is it up to me to test e.g.
> modifiers first?
> 2. How tests should look like?
> E.g. under /lib/tests/modifier_stack/ are .blend files just showing, how
> modifier is supposed to affect given mesh (e.g. curve_modifier.blend;
> which in fact is subsurf + curve combination) and the other ones
> preparing scene, applying modifier and calling validate() on resulting
> mesh (array_test.blend). There is also
> /blender/tests/python/bl_mesh_modifiers.py file, with a comment:
> # Currently this script only generates images from different modifier
> # combinations and does not validate they work correctly,
> # this is because we don't get 1:1 match with bmesh.
> #
> # Later, we may have a way to check the results are valid.
> I don't understand, what does it exactly mean "we don't get 1:1 match
> with bmesh", but this comment is from 2012, so I assume that's not true
> any more.
> The goal of "Tests for Regressions" project is to actually check
> results, so... I've started writing a test for Array modifier, created
> an object, then another - expected one - and in test, I've applied the
> modifier and I've compared the result with the expected mesh using
> bpy.types.Mesh.unit_test_compare(), which, as I've seen, compares data
> like vertices, edges and so on of two meshes (I haven't found many uses
> of that method in tests).
> Should a test in this project look like this?
I have found a convenient way to test end-to-end operation of mesh
operations is to do what you said here (using unit_test_compare).
I wrote a mesh_ops.test.py which is in lib/tests/modeling that is a kind
of framework for specifying mesh ops to apply to different objects
with different elements selected, and the expected output meshes,
and then uses unit_test_compare to compare them.
Examples of use of this are in bevel_regression.blend and
bool_regression.blend in that directory (test specs are in
a text window).
The 'make test' target for blender can specify running blender
on these files and running a function such that success / failure
is tested in the usual way.

> 3. Where they should be placed: .blend or .py?
> I can create expected object using Python by giving vertices/joining
> primitives for some tests. They can be also, probably faster, created
> using GUI.
> What's recommended?
> Creating a .blend file is much easier and more convenient for reviewing
> what's happening in Blender, but it makes harder checking the actual
> code/scene details (like objects' positions, modifiers parameters) and
> searching for it (I haven't found any tool to grep a text inside .blend
> file; only blendfile.py, which as I see, can be used to do so with a
> not-so-little effort). Moreover, I think it's easier to organize tests
> in .py file. In .blend one idea is to use layers (?) to separate tests
> for different parameters (e.g. for array modifier I'd like to test merge
> option and constant offset separately).
> 4. How it will be evaluated, i.e. how much a participant is supposed to
> achieve by each evaluation?
> Will it be set by number of tests/coverage (I've got no idea how to
> check it)? Is it up to me to set milestones with a mentor, basing on my
> intuition, how much time testing each area will take?
> Regards,
> Łukasz Hryniuk
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