[Scons-users] Build and run unit tests automatically on target build

[Andrew C. Morrow]

On Mon, Jun 17, 2024 at 3:27 PM Matthew Ryan <mjr at centauri.org> wrote:

> I've been looking for some way of building and running a unit test
> after another target is run, but so far have been unable to come up
> with a recipe.
>
> The specific example is that of a C/C++ static library built by
> `env.Library()` - I want a setup where, whenever the static library is
> rebuilt, a unit test (built by `env.Program` and linked against the
> static library) is built and run automatically, and if it fails, the
> build fails, so anything later on that links against libfoo would not
> build.
>
> Is such a thing possible?
>

I think it is definitely possible.

What you are trying to express amounts, I think, to the following: if
target B depends on target A, then target B also depends on building and
passing the test for target A. Now, there may be many B, C, D, ... which
all depend on A, and you only want the test to run once. So you don't
really want to depend on running test A so much as you want to depend on
the results of running test A. So the dependency graph looks like:

A < {B, C, D ... }
A < A_test < A_test_proof < { B, C, D, ... }

Where `A_test_proof` is a target which runs A_test, stores the result, and
builds or fails based on the result.

So now the trick is to have the existence of an A < B edge automatically
induce an edge A_test_proof < B. You can do this, perhaps, by writing and
adding a target scanner to the Library builder. One very nice property of
what you are proposing is that it will work with CacheDir, such that if
library A is altered and then restored, test results should be able to be
cached, as can Library objects which depend on those test results.

For some prior art on adding "proof" targets of that type, see
https://github.com/mongodb/mongo/blob/e75ae66953915b7d0d63188268bbf10497b40c65/site_scons/site_tools/mongo_test_execution.py.
It works a little differently because it doesn't automatically make the
build depend on passing tests and just creates aliases, but it should show
how to build the targets for executing the tests in a way that respects
caching. For some related art on automatically adding dependencies with a
scanner, see
https://github.com/mongodb/mongo/blob/8a7b5d451fd706a2ff0ad6c43c3a1f7c88264070/site_scons/site_tools/forceincludes.py

Note that I don't think you want to make building the actual liba.a or
whatever require running the test. There might be good reasons sometimes to
want to produce just the library file as a target without failing the
build. That's why I like the idea of making the requirement be that it is
only use of the library in another target that automates execution of the
associated test.

You can probably also make use of Emitters to automate creation of the test.

What I'm suggesting is probably only one of many ways to get SCons to do
what you are suggesting.
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