oeqa/bblayers.py: add tests for adding new built-in fragments

Add discussed in [1], our best option for customizing built-in fragments
is to pass them from a layer configuration. In short, the reason is that
our statement must be parsed before the addfragments call is parsed.We
also have to use the :append override as using += would override the
original definition of OE_FRAGMENTS_BUILTIN (since it uses a ?=
assignment).

Provide a test case for customizing built-in fragments with
meta-selftest.

[1]: https://lore.kernel.org/yocto-docs/20250925-fragments-v1-0-c9f747361fb2@bootlin.com/T/#m9f7c9f110c084eba17e0f64d8b2ac7a88af3f38e

Cc: Alexander Kanavin <alex.kanavin@gmail.com>
(From OE-Core rev: 38cbf4c0ce5173dc3080fa0fbb3ec3e7926c8137)

Signed-off-by: Antonin Godard <antonin.godard@bootlin.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/meta-selftest/conf/layer.conf b/meta-selftest/conf/layer.conf
index ecc45ded8c..de7d6340ed 100644
--- a/meta-selftest/conf/layer.conf
+++ b/meta-selftest/conf/layer.conf
@@ -12,3 +12,5 @@ BBFILE_PRIORITY_selftest = "5"
 addpylib ${LAYERDIR}/lib oeqa
 
 LAYERSERIES_COMPAT_selftest = "whinlatter"
+
+OE_FRAGMENTS_BUILTIN:append = " selftest-fragment:SELFTEST_BUILTIN_FRAGMENT_VARIABLE"