However, having widgets in unit tests is typically a bad smell. There should be no logic in your GUI widgets, so testing them shouldn’t make sense. GUI objects typically need user interaction, which is not something you can automate (and which may get you in trouble with the Qt event loop too). Try to pull all the non-GUI stuff out of your widget.

this is my code:

class MyFirstClassTest : public QObject
{
Q_OBJECT

private slots:
void initTestCase() {
}

void cleanupTestCase() {
}

void testMyMethod() {
CustomSlider* slider;
slider = new CustomSlider(NULL);
slider->setSpacing(8);
QCOMPARE(slider->spacing(), 8);
}
};

and this is the error:

********* Start testing of MyFirstClassTest *********
Config: Using QTest library 4.5.2, Qt 4.5.2
PASS : MyFirstClassTest::initTestCase()
QFATAL : MyFirstClassTest::testMyMethod() QWidget: Cannot create a QWidget when no GUI is being used
FAIL! : MyFirstClassTest::testMyMethod() Received a fatal error.
Loc: [Unknown file(0)]
Totals: 1 passed, 1 failed, 0 skipped
********* Finished testing of MyFirstClassTest *********