Broken autotest in ktexteditor

[David Faure]

I'm seeing the same thing as the CI: completion_test completely fails.
https://build.kde.org/job/kdeclarative%20master%20stable-kf5-qt5/PLATFORM=Linux,compiler=gcc/31/

frameworks/ktexteditor/autotests>./completion_test testFilterEmptyRange
********* Start testing of CompletionTest *********
Config: Using QtTest library 5.5.1, Qt 5.5.1 (x86_64-little_endian-lp64 shared (dynamic) debug build; by GCC 4.8.3 20140627 [gcc-4_8-branch revision 212064])
PASS   : CompletionTest::initTestCase()
QDEBUG : CompletionTest::testFilterEmptyRange() completion_test(31034)/kf5.kservice.sycoca KSycocaPrivate::openDatabase: Trying to open ksycoca from "/home/dfaure/.cache/ksycoca5"
QDEBUG : CompletionTest::testFilterEmptyRange() completion_test(31034)/kf5.kservice.sycoca checkTimestamps: checking file timestamps
QDEBUG : CompletionTest::testFilterEmptyRange() completion_test(31034)/default CodeCompletionTestModel::completionInvoked: "a"
FAIL!  : CompletionTest::testFilterEmptyRange() Compared values are not the same
   Actual   (countItems(model)): 0
   Expected (40)               : 40
   Loc: [/d/kde/src/5/frameworks/ktexteditor/autotests/src/completion_test.cpp(117)]
PASS   : CompletionTest::cleanupTestCase()
Totals: 2 passed, 1 failed, 0 skipped, 0 blacklisted
********* Finished testing of CompletionTest *********

I tried going back to older git commits to bisect a regression, but I can go back really far and it always just fails
(while CI only turned red two builds ago).
Maybe the bug isn't in the ktexteditor code itself then, but in one of its dependencies?

Can someone who knows how this stuff works, debug it?

-- 
David Faure, faure at kde.org, http://www.davidfaure.fr
Working on KDE Frameworks 5