I am not sure where qtestlib gets the distro definitions from, but here are some lines from /etc/os-release:

NAME="openSUSE Tumbleweed"
# VERSION="20211127"
ID="opensuse-tumbleweed"
ID_LIKE="opensuse suse"
VERSION_ID="20211127"
PRETTY_NAME="openSUSE Tumbleweed"

Please note that the ID_LIKE line includes "opensuse" and "suse" so maybe these should be considered by qtestlib.

In order to match the BLACKLIST file I have to write in full "opensuse-tumbleweed". I also tried using wildcards ("opensuse*" or "opensuse.*"), but with no luck.

EDIT:
A bit of gdb-ing later, and I see that qtestlib gets the system's keywords by invoking

• QSysInfo::productType().toLower().toUtf8() --> "opensuse-tumbleweed"
• QSysInfo::productVersion() --> "20211127"

src/testlib/qtestblacklist.cpp

static QSet<QByteArray> activeConditions()
{
    QSet<QByteArray> result = keywords();

    QByteArray distributionName = QSysInfo::productType().toLower().toUtf8();
    QByteArray distributionRelease = QSysInfo::productVersion().toLower().toUtf8();

And productType() ends up invoking readOsRelease() which apparently gets the ID from /etc/os-release.