Chapter 1: Writing a Unit Test

Writing a Test

Let's assume you want to test the behavior of our QString class. First, you need a class that contains your test functions. This class has to inherit from QObject:

 #include <QtTest/QtTest>

 class TestQString: public QObject
 {
     Q_OBJECT
 private slots:
     void toUpper();
 };

Note that you need to include the QTest header, and that the test functions have to be declared as private slots so the test framework finds and executes it.

Then you need to implement the test function itself. The implementation could look like this:

 void TestQString::toUpper()
 {
     QString str = "Hello";
     QVERIFY(str.toUpper() == "HELLO");
 }

The QVERIFY() macro evaluates the expression passed as its argument. If the expression evaluates to true, the execution of the test function continues. Otherwise, a message describing the failure is appended to the test log, and the test function stops executing.

But if you want a more verbose output to the test log, you should use the QCOMPARE() macro instead:

 void TestQString::toUpper()
 {
     QString str = "Hello";
     QCOMPARE(str.toUpper(), QString("HELLO"));
 }

If the strings are not equal, the contents of both strings is appended to the test log, making it immediately visible why the comparison failed.

Finally, to make our test case a stand-alone executable, the following two lines are needed:

 QTEST_MAIN(TestQString)
 #include "testqstring.moc"

The QTEST_MAIN() macro expands to a simple main() method that runs all the test functions. Note that if both the declaration and the implementation of our test class are in a .cpp file, we also need to include the generated moc file to make Qt's introspection work.

 /myTestDirectory$ qmake -project "CONFIG += qtestlib"
 /myTestDirectory$ qmake
 /myTestDirectory$ make

 ********* Start testing of TestQString *********
 Config: Using QTest library 4.1.0, Qt 4.1.0
 PASS   : TestQString::initTestCase()
 PASS   : TestQString::toUpper()
 PASS   : TestQString::cleanupTestCase()
 Totals: 3 passed, 0 failed, 0 skipped
 ********* Finished testing of TestQString *********