I've created a custom widget plugin. The plugin integrates fine with Qt Creator but when I compile the program, I'm getting this error:

"test.h: No such file or directory"

Where test.h is the name of the custom widget. What am I doing wrong? This is the *.pro file of the application:

TEMPLATE = app
SOURCES += main.cpp \
    mainwindow.cpp
HEADERS += mainwindow.h
FORMS += mainwindow.ui

This is the *.pro file of the plugin:

CONFIG      += designer plugin debug_and_release
TARGET      = $$qtLibraryTarget(testplugin)
TEMPLATE    = lib
HEADERS     = testplugin.h
SOURCES     = testplugin.cpp
RESOURCES   = icons.qrc
target.path = $$[QT_INSTALL_PLUGINS]/designer
INSTALLS    += target
include(test.pri)