Chapter 1: Writing a Unit Test

In this first chapter we will see how to write a simple unit test for a class, and how to execute it.

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 <QTest>

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

Note: You need to include the QTest header and declare the test functions 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 are 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.

Executing a Test

Now that we finished writing our test, we want to execute it. Assuming that our test was saved as testqstring.cpp in an empty directory, we build the test using qmake to create a project and generate a makefile.

 /myTestDirectory$ qmake -project "QT += testlib"
 /myTestDirectory$ qmake
 /myTestDirectory$ make

Note: If you're using windows, replace make with nmake or whatever build tool you use.

Running the resulting executable should give you the following output:

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

Congratulations! You just wrote and executed your first unit test using the Qt Test framework.

Example project @ code.qt.io