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Qt Test Overview

Overview of the Qt unit testing framework.

Qt Test is a framework for unit testing Qt based applications and libraries. Qt Test provides all the functionality commonly found in unit testing frameworks as well as extensions for testing graphical user interfaces.

Qt Test is designed to ease the writing of unit tests for Qt based applications and libraries:

Feature	Details
Lightweight	Qt Test consists of about 6000 lines of code and 60 exported symbols.
Self-contained	Qt Test requires only a few symbols from the Qt Core module for non-gui testing.
Rapid testing	Qt Test needs no special test-runners; no special registration for tests.
Data-driven testing	A test can be executed multiple times with different test data.
Basic GUI testing	Qt Test offers functionality for mouse and keyboard simulation.
Benchmarking	Qt Test supports benchmarking and provides several measurement back-ends.
IDE friendly	Qt Test outputs messages that can be interpreted by Qt Creator, Visual Studio, and KDevelop.
Thread-safety	The error reporting is thread safe and atomic.
Type-safety	Extensive use of templates prevent errors introduced by implicit type casting.
Easily extendable	Custom types can easily be added to the test data and test output.

You can use a Qt Creator wizard to create a project that contains Qt tests and build and run them directly from Qt Creator. For more information, see Qt Creator: Build and Run Tests.

Creating a Test

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. 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(QObject):

    Q_OBJECT
# private
    def myCondition():

        return True

# private slots
    def initTestCase():

        qDebug("Called before everything else.")

    def myFirstTest():

        QVERIFY(True) # check that a condition is satisfied
        QCOMPARE(1, 1) # compare two values

    def mySecondTest():

        QVERIFY(myCondition())
        QVERIFY(1 != 2)

    def 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 .

Increasing Test Function Timeout

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.

Qt Test Command Line Arguments

Syntax

The syntax to execute an autotest takes the following simple form:

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

Substitute testname with the name of your executable. testfunctions can contain names of test functions to be executed. If no testfunctions are passed, all tests are run. If you append the name of an entry in testdata, the test function will be run only with that test data.

For example:

/myTestDirectory$ testQString toUpper

Runs the test function called toUpper with all available test data.

/myTestDirectory$ testQString toUpper toInt:zero

Runs the toUpper test function with all available test data, and the toInt test function with the test data row called zero (if the specified test data doesn’t exist, the associated test will fail and the available data tags are reported).

/myTestDirectory$ testMyWidget -vs -eventdelay 500

Runs the testMyWidget function test, outputs every signal emission and waits 500 milliseconds after each simulated mouse/keyboard event.

Options

Logging Options

The following command line options determine how test results are reported:

• -o filename,format Writes output to the specified file, in the specified format (one of txt, csv, junitxml, xml, lightxml, teamcity or tap). Use the special filename - (hyphen) to log to standard output.

• -o filename Writes output to the specified file.

• -txt Outputs results in plain text.

• -csv Outputs results as comma-separated values (CSV) suitable for import into spreadsheets. This mode is only suitable for benchmarks, since it suppresses normal pass/fail messages.

• -junitxml Outputs results as a JUnit XML document.

• -xml Outputs results as an XML document.

• -lightxml Outputs results as a stream of XML tags.

• -teamcity Outputs results in TeamCity format.

• -tap Outputs results in Test Anything Protocol (TAP) format.

The first version of the -o option may be repeated in order to log test results in multiple formats, but no more than one instance of this option can log test results to standard output.

If the first version of the -o option is used, neither the second version of the -o option nor the -txt, -xml, -lightxml, -teamcity, -junitxml or -tap options should be used.

If neither version of the -o option is used, test results will be logged to standard output. If no format option is used, test results will be logged in plain text.

Test Log Detail Options

The following command line options control how much detail is reported in test logs:

• -silent Silent output; only shows fatal errors, test failures and minimal status messages.

• -v1 Verbose output; shows when each test function is entered. (This option only affects plain text output.)

• -v2 Extended verbose output; shows each QCOMPARE() and QVERIFY() . (This option affects all output formats and implies -v1 for plain text output.)

• -vs Shows all signals that get emitted and the slot invocations resulting from those signals. (This option affects all output formats.)

Testing Options

The following command-line options influence how tests are run:

• -functions Outputs all test functions available in the test, then quits.

• -datatags Outputs all data tags available in the test. A global data tag is preceded by ‘ __global__ ‘.

• -eventdelay ms If no delay is specified for keyboard or mouse simulation ( keyClick() , mouseClick() etc.), the value from this parameter (in milliseconds) is substituted.

• -keydelay ms Like -eventdelay, but only influences keyboard simulation and not mouse simulation.

• -mousedelay ms Like -eventdelay, but only influences mouse simulation and not keyboard simulation.

• -maxwarnings number Sets the maximum number of warnings to output. 0 for unlimited, defaults to 2000.

• -nocrashhandler Disables the crash handler on Unix platforms. On Windows, it re-enables the Windows Error Reporting dialog, which is turned off by default. This is useful for debugging crashes.

• -repeat n Run the testsuite n times or until the test fails. Useful for finding flaky tests. If negative, the tests are repeated forever. This is intended as a developer tool, and is only supported with the plain text logger.

• -skipblacklisted Skip the blacklisted tests. This option is intended to allow more accurate measurement of test coverage by preventing blacklisted tests from inflating coverage statistics. When not measuring test coverage, it is recommended to execute blacklisted tests to reveal any changes in their results, such as a new crash or the issue that caused blacklisting being resolved.

• -platform name This command line argument applies to all Qt applications, but might be especially useful in the context of auto-testing. By using the “offscreen” platform plugin (-platform offscreen) it’s possible to have tests that use QWidget or QWindow run without showing anything on the screen. Currently the offscreen platform plugin is only fully supported on X11.

Benchmarking Options

The following command line options control benchmark testing:

• -callgrind Uses Callgrind to time benchmarks (Linux only).

• -tickcounter Uses CPU tick counters to time benchmarks.

• -eventcounter Counts events received during benchmarks.

• -minimumvalue n Sets the minimum acceptable measurement value.

• -minimumtotal n Sets the minimum acceptable total for repeated executions of a test function.

• -iterations n Sets the number of accumulation iterations.

• -median n Sets the number of median iterations.

• -vb Outputs verbose benchmarking information.

Miscellaneous Options

• -help Outputs the possible command line arguments and gives some useful help.

Qt Test Environment Variables

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 was added in Qt 6.1.

• QTEST_THROW_ON_FAIL (since 6.8) Setting this variable to a non-zero value will cause QCOMPARE() / QVERIFY() etc to throw on failure (as opposed to just returning from the immediately-surrounding function scope).

• QTEST_THROW_ON_SKIP (since 6.8) Same as QTEST_THROW_ON_FAIL, except affecting QSKIP() .

Creating a Benchmark

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

class MyFirstBenchmark(QObject):

    Q_OBJECT
# private slots
    def myFirstBenchmark():

        string1 = QString()
        string2 = QString()
        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

The code inside the QBENCHMARK macro will be measured, and possibly also repeated several times in order to get an accurate measurement. This depends on the selected measurement back-end. Several back-ends are available. They can be selected on the command line:

Name	Command-line Argument	Availability
Walltime	(default)	All platforms
CPU tick counter	-tickcounter	Windows, macOS, Linux, many UNIX-like systems.
Event Counter	-eventcounter	All platforms
Valgrind Callgrind	-callgrind	Linux (if installed)
Linux Perf	-perf	Linux

In short, walltime is always available but requires many repetitions to get a useful result. Tick counters are usually available and can provide results with fewer repetitions, but can be susceptible to CPU frequency scaling issues. Valgrind provides exact results, but does not take I/O waits into account, and is only available on a limited number of platforms. Event counting is available on all platforms and it provides the number of events that were received by the event loop before they are sent to their corresponding targets (this might include non-Qt events).

The Linux Performance Monitoring solution is available only on Linux and provides many different counters, which can be selected by passing an additional option -perfcounter countername, such as -perfcounter cache-misses, -perfcounter branch-misses, or -perfcounter l1d-load-misses. The default counter is cpu-cycles. The full list of counters can be obtained by running any benchmark executable with the option -perfcounterlist.

• Using the performance counter may require enabling access to non-privileged applications.

• Devices that do not support high-resolution timers default to one-millisecond granularity.

See Writing a Benchmark in the Qt Test Tutorial for more benchmarking examples.

Using Global Test Data

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():

def roundTripInt(self):

    QFETCH_GLOBAL(QLocale, locale)
    QFETCH(int, number)
    ok = bool()
    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.