Qt Test Overview

To create a test, subclass QObject and add one or more private slots to it. Each private slot is a test function in your test. QTest::qExec() can be used to execute all test functions in the test object.

In addition, you can define the following private slots that are not treated as test functions. When present, they will be executed by the testing framework and can be used to initialize and clean up either the entire test or the current test function.

• initTestCase() will be called before the first test function is executed.

• initTestCase_data() will be called to create a global test data table.

• cleanupTestCase() will be called after the last test function was executed.

• init() will be called before each test function is executed.

• cleanup() will be called after every test function.

Use initTestCase() for preparing the test. Every test should leave the system in a usable state, so it can be run repeatedly. Cleanup operations should be handled in cleanupTestCase(), so they get run even if the test fails.

Use init() for preparing a test function. Every test function should leave the system in a usable state, so it can be run repeatedly. Cleanup operations should be handled in cleanup(), so they get run even if the test function fails and exits early.

Alternatively, you can use RAII (resource acquisition is initialization), with cleanup operations called in destructors, to ensure they happen when the test function returns and the object moves out of scope.

If initTestCase() fails, no test function will be executed. If init() fails, the following test function will not be executed, the test will proceed to the next test function.

Example:

class MyFirstTest: public QObject
{
    Q_OBJECT

private:
    bool myCondition()
    {
        return true;
    }

private slots:
    void initTestCase()
    {
        qDebug("Called before everything else.");
    }

    void myFirstTest()
    {
        QVERIFY(true); // check that a condition is satisfied
        QCOMPARE(1, 1); // compare two values
    }

    void mySecondTest()
    {
        QVERIFY(myCondition());
        QVERIFY(1 != 2);
    }

    void cleanupTestCase()
    {
        qDebug("Called after myFirstTest and mySecondTest.");
    }
};

Finally, if the test class has a static public void initMain() method, it is called by the QTEST_MAIN macros before the QApplication object is instantiated. This was added in 5.14.

For more examples, refer to the Qt Test Tutorial.

QtTest limits the run-time of each test to catch infinite loops and similar bugs. By default, any test function call will be interrupted after five minutes. For data-driven tests, this applies to each call with a distinct data-tag. This timeout can be configured by setting the QTEST_FUNCTION_TIMEOUT environment variable to the maximum number of milliseconds that is acceptable for a single call to take. If a test takes longer than the configured timeout, it is interrupted, and qFatal() is called. As a result, the test aborts by default, as if it had crashed.

To set QTEST_FUNCTION_TIMEOUT from the command line on Linux or macOS, enter:

QTEST_FUNCTION_TIMEOUT=900000
export QTEST_FUNCTION_TIMEOUT

On Windows:

SET QTEST_FUNCTION_TIMEOUT=900000

Then run the test inside this environment.

Alternatively, you can set the environment variable programmatically in the test code itself, for example by calling, from the initMain() special method of your test class:

qputenv("QTEST_FUNCTION_TIMEOUT", "900000");

To calculate a suitable value for the timeout, see how long the test usually takes and decide how much longer it can take without that being a symptom of some problem. Convert that longer time to milliseconds to get the timeout value. For example, if you decide that a test that takes several minutes could reasonably take up to twenty minutes, for example on a slow machine, multiply 20 * 60 * 1000 = 1200000 and set the environment variable to 1200000 instead of the 900000 above.

You can build an executable that contains one test class that typically tests one class of production code. However, usually you would want to test several classes in a project by running one command.

See Writing a Unit Test for a step by step explanation.

Building with CMake and CTest▲

project(mytest LANGUAGES CXX)

find_package(Qt6 REQUIRED COMPONENTS Test)

set(CMAKE_INCLUDE_CURRENT_DIR ON)

set(CMAKE_AUTOMOC ON)

enable_testing(true)

add_executable(mytest tst_mytest.cpp)
add_test(NAME mytest COMMAND mytest)

target_link_libraries(mytest PRIVATE Qt::Test)

Building with qmake▲

QT += testlib

CONFIG += testcase

CONFIG += no_testcase_installs

Building with Other Tools▲

Syntax▲

testname [options] [testfunctions[:testdata]]...

/myTestDirectory$ testQString toUpper

/myTestDirectory$ testQString toUpper toInt:zero

/myTestDirectory$ testMyWidget -vs -eventdelay 500

Options▲

You can set certain environment variables in order to affect the execution of an autotest:

• QTEST_DISABLE_CORE_DUMP Setting this variable to a non-zero value will disable the generation of a core dump file.

• QTEST_DISABLE_STACK_DUMP Setting this variable to a non-zero value will prevent Qt Test from printing a stacktrace in case an autotest times out or crashes.

• QTEST_FATAL_FAIL Setting this variable to a non-zero value will cause a failure in an autotest to immediately abort the entire autotest. This is useful to e.g. debug an unstable or intermittent failure in a test, by launching the test in a debugger. Support for this variable has been added in Qt 6.1.

To create a benchmark, follow the instructions for creating a test and then add a QBENCHMARK macro or QTest::setBenchmarkResult() to the test function that you want to benchmark. In the following code snippet, the macro is used:

class MyFirstBenchmark: public QObject
{
    Q_OBJECT
private slots:
    void myFirstBenchmark()
    {
        QString string1;
        QString string2;
        QBENCHMARK {
            string1.localeAwareCompare(string2);
        }
    }
};

A test function that measures performance should contain either a single QBENCHMARK macro or a single call to setBenchmarkResult(). Multiple occurrences make no sense, because only one performance result can be reported per test function, or per data tag in a data-driven setup.

Avoid changing the test code that forms (or influences) the body of a QBENCHMARK macro, or the test code that computes the value passed to setBenchmarkResult(). Differences in successive performance results should ideally be caused only by changes to the product you are testing. Changes to the test code can potentially result in misleading report of a change in performance. If you do need to change the test code, make that clear in the commit message.

In a performance test function, the QBENCHMARK or setBenchmarkResult() should be followed by a verification step using QCOMPARE(), QVERIFY(), and so on. You can then flag a performance result as invalid if another code path than the intended one was measured. A performance analysis tool can use this information to filter out invalid results. For example, an unexpected error condition will typically cause the program to bail out prematurely from the normal program execution, and thus falsely show a dramatic performance increase.

Selecting the Measurement Back-end▲

You can define initTestCase_data() to set up a global test data table. Each test is run once for each row in the global test data table. When the test function itself is data-driven, it is run for each local data row, for each global data row. So, if there are g rows in the global data table and d rows in the test's own data-table, the number of runs of this test is g times d.

Global data is fetched from the table using the QFETCH_GLOBAL() macro.

The following are typical use cases for global test data:

• Selecting among the available database backends in QSql tests to run every test against every database.

• Doing all networking tests with and without SSL (HTTP versus HTTPS) and proxying.

• Testing a timer with a high precision clock and with a coarse one.

• Selecting whether a parser shall read from a QByteArray or from a QIODevice.

For example, to test each number provided by roundTripInt_data() with each locale provided by initTestCase_data():

void TestQLocale::roundTripInt()
{
    QFETCH_GLOBAL(QLocale, locale);
    QFETCH(int, number);
    bool ok;
    QCOMPARE(locale.toInt(locale.toString(number), &ok), number);
    QVERIFY(ok);
}

On the command-line of a test you can pass the name of a function (with no test-class-name prefix) to run only that one function's tests. If the test class has global data, or the function is data-driven, you can append a data tag, after a colon, to run only that tag's data-set for the function. To specify both a global tag and a tag specific to the test function, combine them with a colon between, putting the global data tag first. For example

./testqlocale roundTripInt:zero

will run the zero test-case of the roundTripInt() test above (assuming its TestQLocale class has been compiled to an executable testqlocale) in each of the locales specified by initTestCase_data(), while

./testqlocale roundTripInt:C

will run all three test-cases of roundTripInt() only in the C locale and

./testqlocale roundTripInt:C:zero

will only run the zero test-case in the C locale.

Providing such fine-grained control over which tests are to be run can make it considerably easier to debug a problem, as you only need to step through the one test-case that has been seen to fail.