git:20260724.d4db756 to git:20260728.1bce424

---

name: qt-test-framework

description: "Authors and runs Qt Test - the first-party C++ unit + GUI test framework that ships with Qt 6 (via the `QtTest` module header). Covers the `QTEST_MAIN` / `QTEST_APPLESS_MAIN` / `QTEST_GUILESS_MAIN` entry-point macros, the `QObject` private-slot test pattern, `QVERIFY` / `QCOMPARE` / `QFETCH` assertions, GUI event simulation (`QTest::mouseClick`, `QTest::keyClick`, `QTest::touchEvent`), `QSignalSpy` for signal introspection, `QBENCHMARK` for performance regression, and the `-o file,junitxml` CI output. Use for in-process testing of Qt widgets, QObject signal/slot chains, and Qt Quick / QML application logic; for out-of-process Qt-app driving, use an OS-native accessibility driver instead."

metadata:

keywords: "qt, qttest, c++, qsignalspy, qbenchmark, widget-testing"

---

# qt-test-framework

## Overview

[qtover]: https://doc.qt.io/qt-6/qtest-overview.html

[qtns]: https://doc.qt.io/qt-6/qtest.html

## When to use

- Pure-logic unit testing of `QObject`-based classes - view models,

data models, signal/slot graphs.

- GUI tests of `QWidget` or Qt Quick views where the test

executable can link the app code (in-process), avoiding the

brittleness of out-of-process accessibility-tree drivers.

- Benchmark + performance-regression checks via `QBENCHMARK`

([qtns][qtns]).

- `QSignalSpy`-based assertions on signal emission order /

arguments ([qtidx][qtidx]).

[qtidx]: https://doc.qt.io/qt-6/qttest-index.html

## Step 1 - Add Qt Test to the build

CMake (Qt 6, the canonical Qt build system per Qt 6 docs):

```cmake

find_package(Qt6 6.5 REQUIRED COMPONENTS Test Widgets)

qt_add_executable(test_calculator tst_calculator.cpp Calculator.cpp)

target_link_libraries(test_calculator PRIVATE Qt6::Test Qt6::Widgets)

add_test(NAME test_calculator COMMAND test_calculator)

```

## Step 2 - Author a test class

The canonical shape per [qtover][qtover] - a `QObject` subclass with

**private slots** as test functions:

```cpp

#include <QtTest/QtTest>

#include "Calculator.h"

class TestCalculator : public QObject {

Q_OBJECT

private slots:

// initTestCase() / cleanupTestCase() run once per class

void initTestCase();

void cleanupTestCase();

// init() / cleanup() run around each test function

void init();

void cleanup();

void addsTwoIntegers();

void emitsResultChangedSignal();

void rejectsDivisionByZero();

};

void TestCalculator::initTestCase() {

qDebug() << "Starting test suite";

}

void TestCalculator::addsTwoIntegers() {

Calculator c;

QCOMPARE(c.add(2, 3), 5); // strict equality assertion

QVERIFY(c.lastError().isEmpty());

}

QTEST_MAIN(TestCalculator) // generates main() + QApplication

#include "tst_calculator.moc" // include moc output

```

The four lifecycle slots are recognised by name ([qtover][qtover]):

`initTestCase` (once before any test), `cleanupTestCase` (once

after), `init` (per test), `cleanup` (per test).

## Step 3 - Pick the right entry-point macro

Per [qtns][qtns], three entry-point macros choose what application

class the harness instantiates:

| Macro | Instantiates | Use for |

|---|---|---|

| `QTEST_MAIN` | `QApplication` | Widget GUI tests |

| `QTEST_GUILESS_MAIN` | `QCoreApplication` | Console / non-GUI logic tests |

| `QTEST_APPLESS_MAIN` | none | Tests of code that itself instantiates its own application object |

Per [qtover][qtover], if the test class defines a static public

`void initMain()` method, "it is called by the QTEST_MAIN macros

before the QApplication object is instantiated" - that's the hook

for setting platform-specific environment variables before Qt's

event loop starts.

## Step 4 - Data-driven tests

Per [qtns][qtns], `QFETCH` retrieves test data values; data is

declared in a sibling `_data()` slot:

```cpp

private slots:

void addsTwoIntegers_data();

void addsTwoIntegers();

void TestCalculator::addsTwoIntegers_data() {

QTest::addColumn<int>("a");

QTest::addColumn<int>("b");

QTest::addColumn<int>("expected");

QTest::newRow("zeros") << 0 << 0 << 0;

QTest::newRow("positives") << 2 << 3 << 5;

QTest::newRow("negatives") << -2 << -3 << -5;

QTest::newRow("overflow") << INT_MAX << 1 << INT_MAX + 1; // documents UB

}

void TestCalculator::addsTwoIntegers() {

QFETCH(int, a);

QFETCH(int, b);

QFETCH(int, expected);

Calculator c;

QCOMPARE(c.add(a, b), expected);

}

```

Per [qtover][qtover]: "A test can be executed multiple times with

different test data." Each `newRow` runs the test function once.

## Step 5 - GUI event simulation

```cpp

void TestLoginWidget::successfulLogin() {

LoginWidget w;

w.show();

QVERIFY(QTest::qWaitForWindowExposed(&w));

QTest::keyClicks(w.usernameField(), "alice");

QTest::keyClicks(w.passwordField(), "s3cret");

QTest::mouseClick(w.submitButton(), Qt::LeftButton);

QTRY_VERIFY(w.isLoggedIn()); // polls until true or times out

QCOMPARE(w.currentUser(), QStringLiteral("alice"));

}

```

`QTRY_VERIFY` / `QTRY_COMPARE` ([qtns][qtns]) poll the predicate

with a default 5-second timeout - the right primitive for waiting on

async signal/slot completion without ad-hoc `QTest::qWait` sleeps.

## Step 6 - Signal introspection with QSignalSpy

Per [qtidx][qtidx], QSignalSpy enables "easy introspection for Qt's

signals and slots":

```cpp

void TestCalculator::emitsResultChangedSignal() {

Calculator c;

QSignalSpy spy(&c, &Calculator::resultChanged);

c.add(2, 3);

QCOMPARE(spy.count(), 1);

const QList<QVariant> args = spy.takeFirst();

QCOMPARE(args.at(0).toInt(), 5);

}

```

This is the canonical pattern for asserting on signal emission

order, count, and argument values - far more robust than connecting

test-internal slots and counting invocations by hand.

## Step 7 - Benchmarks

## Step 8 - Run

Per [qtover][qtover], a Qt Test executable accepts the following

command-line options:

```bash

# List all test functions

./test_calculator -functions

# Extended verbose - shows each QCOMPARE / QVERIFY

./test_calculator -v2

# Run a specific test function

./test_calculator addsTwoIntegers

# Run a specific data row

./test_calculator addsTwoIntegers:negatives

# Write JUnit XML for CI ingestion

./test_calculator -o results.xml,junitxml

```

The `-o filename,format` flag per [qtover][qtover] supports formats:

"txt, csv, junitxml, xml, lightxml, teamcity, or tap".

For multi-binary suites, `ctest` (driven by `add_test` from Step 1)

runs the per-test executables and aggregates outcomes.

## Step 9 - Parsing results

```bash

./test_calculator -o results-junit.xml,junitxml

```

The JUnit XML output feeds

`junit-xml-analysis`

for cross-platform aggregation alongside other JUnit-emitting test

runners.

## Step 10 - CI integration

## Anti-patterns

| Anti-pattern | Why it fails | Fix |

|---|---|---|

| Public slots as test functions | moc treats them as Qt signals/slots; harness ignores them | Private slots ([qtover][qtover]) |

| Forgetting `#include "tst_xxx.moc"` for single-file tests | Linker error - moc output not bundled | Include the generated moc file at the bottom of the .cpp (Step 2) |

| `QTest::qWait(2000)` between actions | Flaky; slow on fast machines, racy on slow | `QTRY_VERIFY` / `QTRY_COMPARE` with predicate polling ([qtns][qtns]) |

| One mega-test slot exercising many flows | First failure stops the chain; coverage attribution lost | One slot per behaviour; share setup via `init()` ([qtover][qtover]) |

| Test depends on `QTimer::singleShot(0, …)` cascade | Event-loop ordering varies | Drive the event loop with `QCoreApplication::processEvents()` or `QTRY_*` predicates |

| Using `QTEST_MAIN` for headless CI | Tries to instantiate `QApplication` without a display | `QTEST_GUILESS_MAIN` for non-widget tests; `QT_QPA_PLATFORM=offscreen` for widget tests (Step 10) |

| QSignalSpy connected after the action | Misses emissions; count is wrong | Construct `QSignalSpy` *before* the action that triggers the signal (Step 6) |

| Benchmarks mixed with correctness tests in the same slot | Iteration count masks regressions | Separate `_benchmark()` slots; gate on regression in CI |

## Limitations

- **In-process only.** Qt Test links the application code into the

test binary; it cannot drive a separately-packaged Qt app - for

that, use an OS-native accessibility driver.

- **No binary compatibility guarantee.** Per [qtidx][qtidx], "no

binary compatibility guarantee" is offered for Qt Test;

recompile when the Qt version changes.

- **`QApplication` singleton constraint.** Multiple `QTEST_MAIN`

test binaries cannot share a process - each test binary runs as

its own executable (which is why `ctest` exists).

- **GUI tests need a display platform.** Headless Linux runners

require `QT_QPA_PLATFORM=offscreen` or `xvfb-run` for widget-

level tests.

- **No async-await ergonomics.** Qt Test predates coroutines; async

flows use `QSignalSpy` + `QTRY_VERIFY` or explicit event-loop

driving - clunkier than Playwright's `await`-everywhere model.

- **Localised string assertions in QCOMPARE** are brittle -

prefer asserting on QString identifiers (object names) or

enum values rather than displayed text.

## References

- Qt Test overview - [qtover][qtover].

- QTest namespace reference - [qtns][qtns].

- Qt Test module index - [qtidx][qtidx].

- Sibling out-of-process Qt drivers:

`winappdriver`,

`xctest-mac-desktop`,

`at-spi-linux`.

- Strategic frame:

`desktop-test-strategy-reference`.

- Downstream:

`junit-xml-analysis`.