top-level cmake build: failed to generate QtTestDepends

$ mkcd ~/dev/qt6-dbg
$ cmake ../qt6 -DBUILD_TESTING=ON -DBUILD_WITH_PCH=OFF -DCMAKE_CXX_COMPILER=/usr/lib/icecream/libexec/icecc/bin/g++ -GNinja
$ ninja
....
[717/9185] Building CXX object qtbase/tests/auto/testlib/selftests/silent/CMakeFiles/silent.dir/tst_silent.cpp.o
FAILED: qtbase/tests/auto/testlib/selftests/silent/CMakeFiles/silent.dir/tst_silent.cpp.o 
/usr/lib/icecream/libexec/icecc/bin/g++ -DQT_CORE_LIB -DQT_NO_EXCEPTIONS -DQT_TESTLIB_LIB -D_LARGEFILE64_SOURCE -D_LARGEFILE_SOURCE -Iqtbase/tests/auto/testlib/selftests/silent/silent_autogen/include -I/home/rutledge/dev/qt6/qtbase/tests/auto/testlib/selftests/silent -Iqtbase/tests/auto/testlib/selftests/silent -Iqtbase/include -Iqtbase/include/QtCore -I/home/rutledge/dev/qt6/qtbase/mkspecs/linux-g++ -Iqtbase/src/testlib -Iqtbase/include/QtTest/6.0.0 -Iqtbase/include/QtTest/6.0.0/QtTest -Iqtbase/src/corelib -Iqtbase/include/QtCore/6.0.0 -Iqtbase/include/QtCore/6.0.0/QtCore -Iqtbase/include/QtTest -O2 -pipe -march=corei7 -g -Og -fPIE -fvisibility=hidden -fvisibility-inlines-hidden -Wall -Wextra -fno-exceptions -fPIC -pthread -Wsuggest-override -std=gnu++17 -MD -MT qtbase/tests/auto/testlib/selftests/silent/CMakeFiles/silent.dir/tst_silent.cpp.o -MF qtbase/tests/auto/testlib/selftests/silent/CMakeFiles/silent.dir/tst_silent.cpp.o.d -o qtbase/tests/auto/testlib/selftests/silent/CMakeFiles/silent.dir/tst_silent.cpp.o -c /home/rutledge/dev/qt6/qtbase/tests/auto/testlib/selftests/silent/tst_silent.cpp
In file included from /home/rutledge/dev/qt6/qtbase/tests/auto/testlib/selftests/silent/tst_silent.cpp:30:
qtbase/include/QtTest/QtTest:3:10: fatal error: QtTest/QtTestDepends: No such file or directory
    3 | #include <QtTest/QtTestDepends>
      |          ^~~~~~~~~~~~~~~~~~~~~~
compilation terminated.
[726/9185] Building CXX object qtbase/src/testlib/CMakeFiles/Test.dir/qtestcase.cpp.o
ninja: build stopped: subcommand failed.