Qt test-unit: Error: undefined reference to `imp__ZN5Q

I am trying to create a "Qt unit test" following this tutorial. I created a new project: Qt Gui Application with a header file as mentioned and a class that contains the test function. I added #CONFIG += testlib to my ".pro" file. However, when I run my code, I get this errors:

In function `simulateEvent':

• error: undefined reference to `_imp___ZN5QTest15defaultKeyDelayEv'
• error: undefined reference to `_imp___ZN5QTest15defaultKeyDelayEv'
• error: undefined reference to `_imp___ZN5QTest5qWarnEPKcS1_i'

then in function 'mouseEvent':

• error: undefined reference to `_imp___ZN5QTest17defaultMouseDelayEv'
• error: undefined reference to `_imp___ZN5QTest17defaultMouseDelayEv'
• error: undefined reference to `_imp___ZN5QTest17defaultMouseDelayEv'
• error: undefined reference to `_imp___ZN5QTest17defaultMouseDelayEv'
• error: undefined reference to `_imp___ZN5QTest5qWarnEPKcS1_i'

then in function 'simulateEvent' again:

• error: undefined reference to `_imp___ZN5QTest15defaultKeyDelayEv'
• error: undefined reference to `_imp___ZN5QTest15defaultKeyDelayEv'
• error: undefined reference to `_imp___ZN5QTest5qWarnEPKcS1_i'

then in function 'mouseEvent' again:

• error: undefined reference to `_imp___ZN5QTest17defaultMouseDelayEv'
• error: undefined reference to `_imp___ZN5QTest17defaultMouseDelayEv'
• error: undefined reference to `_imp___ZN5QTest17defaultMouseDelayEv'
• error: undefined reference to `_imp___ZN5QTest17defaultMouseDelayEv'
• error: undefined reference to `_imp___ZN5QTest5qWarnEPKcS1_i'

I could not find any explanation for this as everything looks right . what am I missing ?

Try QT += testlib, without starting #