Chapter 2: Data Driven Testing

This chapter demonstrates how to execute a test multiple times with different test data.

So far, we have hard coded the data we wanted to test into our test function. If we add more test data, the function might look like this:

QCOMPARE(QString("hello").toUpper(), QString("HELLO"));
QCOMPARE(QString("Hello").toUpper(), QString("HELLO"));
QCOMPARE(QString("HellO").toUpper(), QString("HELLO"));
QCOMPARE(QString("HELLO").toUpper(), QString("HELLO"));

To prevent the function from being cluttered with repetitive code, Qt Test supports adding test data to a test function. All we need is to add another private slot to our test class:

class TestQString: public QObject
{
    Q_OBJECT

private slots:
    void toUpper_data();
    void toUpper();
};

Writing the Data Function

A test function's associated data function has _data appended to its name. Our data function looks like this:

void TestQString::toUpper_data()
{
    QTest::addColumn<QString>("string");
    QTest::addColumn<QString>("result");

    QTest::newRow("all-lower") << "hello" << "HELLO";
    QTest::newRow("mixed")     << "Hello" << "HELLO";
    QTest::newRow("all-upper") << "HELLO" << "HELLO";
}

First, we define the two elements of our test table using the QTest::addColumn() function: a test string and the expected result of applying the QString::toUpper() function to that string.

Then, we add some data to the table using the QTest::newRow() function. We can also use QTest::addRow() if we need to format some data in the row name, for example when generating many data rows iteratively. Each row of data will become a separate row in the test table.

QTest::newRow() takes one argument: a name that will be associated with the data set and used in the test log to identify the data row. QTest::addRow() takes a (printf-style) format string followed by the parameters to be represented in place of the formatting tokens in the format string. Then, we stream the data set into the new table row. First an arbitrary string, and then the expected result of applying the QString::toUpper() function to that string.

You can think of the test data as a two-dimensional table. In our case, it has two columns called string and result and three rows. In addition, a name and an index are associated with each row:

When data is streamed into the row, each datum is asserted to match the type of the column whose value it supplies. If any assertion fails, the test is aborted.

The names of rows and columns, in a given test function's data table, should be unique: if two rows share a name, or two columns share a name, a warning will (since Qt 6.5) be produced. See qWarning() for how you can cause warnings to be treated as errors and Test for Warnings for how to get your tests clear of other warnings.

Rewriting the Test Function

Our test function can now be rewritten:

void TestQString::toUpper()
{
    QFETCH(QString, string);
    QFETCH(QString, result);

    QCOMPARE(string.toUpper(), result);
}

The TestQString::toUpper() function will be executed three times, once for each entry in the test table that we created in the associated TestQString::toUpper_data() function.

First, we fetch the two elements of the data set using the QFETCH() macro. QFETCH() takes two arguments: The data type of the element and the element name. Then, we perform the test using the QCOMPARE() macro.

This approach makes it very easy to add new data to the test without modifying the test itself.

Preparing the Stand-Alone Executable

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

QTEST_MAIN(TestQString)
#include "testqstring.moc"

As before, the QTEST_MAIN() macro expands to a simple main() method that runs all the test functions, and since 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: BSD-3-Clause

cmake_minimum_required(VERSION 3.16)
project(tutorial2 LANGUAGES CXX)

if(NOT DEFINED INSTALL_EXAMPLESDIR)
    set(INSTALL_EXAMPLESDIR "examples")
endif()

set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/qtestlib/tutorial2")

find_package(Qt6 REQUIRED COMPONENTS Core Gui Test Widgets)

qt_standard_project_setup()

qt_add_executable(tutorial2
    testqstring.cpp
)

set_target_properties(tutorial2 PROPERTIES
    WIN32_EXECUTABLE TRUE
    MACOSX_BUNDLE TRUE
)

target_link_libraries(tutorial2 PRIVATE
    Qt6::Core
    Qt6::Gui
    Qt6::Test
    Qt6::Widgets
)

install(TARGETS tutorial2
    RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
)

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/tutorial2
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(all-lower)
PASS   : TestQString::toUpper(mixed)
PASS   : TestQString::toUpper(all-upper)
PASS   : TestQString::cleanupTestCase()
Totals: 5 passed, 0 failed, 0 skipped, 0 blacklisted, 0ms
********* Finished testing of TestQString *********

Example project @ code.qt.io