Chapter 1: Writing a Unit Test

This first chapter demonstrates how to write a simple unit test and how to run the test case as a stand-alone executable.

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();
 };

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.

Preparing the Stand-Alone Executable

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.

Building the Executable

You can build the test case executable using CMake or qmake.

Building with CMake

Configure your build settings in your CMakeLists.txt file:

 # Copyright (C) 2022 The Qt Company Ltd.
 # SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

 cmake_minimum_required(VERSION 3.16)
 project(tutorial1 LANGUAGES CXX)

 find_package(Qt6 REQUIRED COMPONENTS Core Gui Test Widgets)

 qt_standard_project_setup()

 qt_add_executable(tutorial1
     testqstring.cpp
 )

 set_target_properties(tutorial1 PROPERTIES
     WIN32_EXECUTABLE TRUE
     MACOSX_BUNDLE TRUE
 )

 target_link_libraries(tutorial1 PRIVATE
     Qt6::Core
     Qt6::Gui
     Qt6::Test
     Qt6::Widgets
 )

 install(TARGETS tutorial1
     BUNDLE  DESTINATION .
     RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR}
     LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
 )

 qt_generate_deploy_app_script(
     TARGET tutorial1
     OUTPUT_SCRIPT deploy_script
     NO_UNSUPPORTED_PLATFORM_ERROR
 )
 install(SCRIPT ${deploy_script})

Next, from the command line, run either cmake or use the qt-cmake convenience script located in Qt-prefix/<version>/<platform>/bin/qt-cmake:

 <Qt-prefix>/<version>/<platform>/bin/qt-cmake <source-dir> <build-dir> -G Ninja

Then, run your preferred generator tool to build the executable. Here, we're using Ninja:

 ninja

Building with qmake

Configure your build settings in your .pro file:

 QT += widgets testlib

 SOURCES = testqstring.cpp

 # install
 target.path = $$[QT_INSTALL_EXAMPLES]/qtestlib/tutorial1
 INSTALLS += target

Next, run qmake, and, finally, run make to build your executable:

 qmake
 make

Running the Executable

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.