tests: Fix Qt dependencies.

Partially fixes
<#882>.
This follows commit dae92490.

* tests/CMakeLists.txt: Rename QML_LIBS to QT_LIBS, a regression
introduced in d82e3820.  Remove the
dependency on on the Widgets module, now provided via QT_LIBS.
* tests/qml/main.cpp [WITH_WEBENGINE]: Include QtWebEngine modules
conditionally.
(main) [WITH_WEBENGINE]: Initialize webengine conditionally.

Change-Id: I0df4e11ca3571338fb1e8967784dc6f09ca1dfee

tests/CMakeLists.txt

-find_package(Qt${QT_VERSION_MAJOR} CONFIG REQUIRED QuickTest Widgets Test)
+find_package(Qt${QT_VERSION_MAJOR} CONFIG REQUIRED QuickTest Test Widgets)
 
 if(MSVC)
     # Download and unpack googletest for windows
@@ -15,7 +15,7 @@ else()
 endif()
 
 enable_testing(true)
-set(QML_TEST_LIBS ${QML_LIBS} Qt::QuickTest Qt::Widgets Qt::Test)
+set(QML_TEST_LIBS ${QT_LIBS} Qt::QuickTest Qt::Test Qt::Widgets)
 set(TESTS_INCLUDES
     ${CMAKE_SOURCE_DIR}/src
     ${CMAKE_SOURCE_DIR}/tests/qml

tests/qml/main.cpp

@@ -31,9 +31,10 @@
 #include <QQmlEngine>
 #include <QQmlContext>
 #include <QFontDatabase>
+#ifdef WITH_WEBENGINE
 #include <QtWebEngineCore>
 #include <QtWebEngineQuick>
-
+#endif
 #ifdef Q_OS_WIN
 #include <windows.h>
 #endif
@@ -155,9 +156,9 @@ main(int argc, char** argv)
         // Adjust the argument count.
         argc = std::distance(argv, end);
     }
-
+#ifdef WITH_WEBENGINE
     QtWebEngineQuick::initialize();
-
+#endif
     QTEST_SET_MAIN_SOURCE_PATH
     Setup setup(muteDring);
     return quick_test_main_with_setup(argc, argv, "qml_test", nullptr, &setup);