Introduce QSignalSpy constructor allows to spy on a meta method

This functionality is especially convenient if meta-object system is
heavily used in a test. For example, if you need to test a bunch of
signals based on their names and/or argument types.

Change-Id: I09a4ecbbd3d0859b5fd466d9dde7679804eb7614
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

3 files changed, 80 insertions, 0 deletions

diff --git a/src/testlib/doc/snippets/code/doc_src_qsignalspy.cpp b/src/testlib/doc/snippets/code/doc_src_qsignalspy.cpp
index a4513a55a9..37aba2715b 100644
--- a/src/testlib/doc/snippets/code/doc_src_qsignalspy.cpp
+++ b/src/testlib/doc/snippets/code/doc_src_qsignalspy.cpp
@@ -98,3 +98,51 @@ QVERIFY(spy.wait(1000));
 QSignalSpy spy(myPushButton, &QPushButton::clicked);
 //! [6]
 
+//! [7]
+QObject object;
+auto mo = object.metaObject();
+auto signalIndex = mo->indexOfSignal("objectNameChanged(QString)");
+auto signal = mo->method(signalIndex);
+
+QSignalSpy spy(&object, signal);
+object.setObjectName("A new object name");
+QCOMPARE(spy.count(), 1);
+//! [7]
+
+//! [8]
+void tst_QWindow::writeMinMaxDimensionalProps_data()
+    QTest::addColumn<int>("propertyIndex");
+
+    // Collect all relevant properties
+    static const auto mo = QWindow::staticMetaObject;
+    for (int i = mo.propertyOffset(); i < mo.propertyCount(); ++i) {
+        auto property = mo.property(i);
+
+        // ...that have type int
+        if (property.type() == QVariant::Int) {
+            static const QRegularExpression re("^minimum|maximum");
+            const auto name = property.name();
+
+            // ...and start with "minimum" or "maximum"
+            if (re.match(name).hasMatch()) {
+                QTest::addRow("%s", name) << i;
+            }
+        }
+    }
+}
+
+void tst_QWindow::writeMinMaxDimensionalProps()
+{
+    QFETCH(int, propertyIndex);
+
+    auto property = QWindow::staticMetaObject.property(propertyIndex);
+    QVERIFY(property.isWritable());
+    QVERIFY(property.hasNotifySignal());
+
+    QWindow window;
+    QSignalSpy spy(&window, property.notifySignal());
+
+    QVERIFY(property.write(&window, 42));
+    QCOMPARE(spy.count(), 1);
+}
+//! [8]
diff --git a/src/testlib/qsignalspy.h b/src/testlib/qsignalspy.h
index 91c2d139a8..dc0c58044f 100644
--- a/src/testlib/qsignalspy.h
+++ b/src/testlib/qsignalspy.h
@@ -118,6 +118,16 @@ public:
     }
 #endif // Q_CLANG_QDOC
 
+    QSignalSpy(const QObject *obj, const QMetaMethod &signal)
+        : m_waiting(false)
+    {
+        if (isObjectValid(obj) && isSignalMetaMethodValid(signal) &&
+            connectToSignal(obj, signal.methodIndex())) {
+            sig = signal.methodSignature();
+            initArgs(signal, obj);
+        }
+    }
+
     inline bool isValid() const { return !sig.isEmpty(); }
     inline QByteArray signal() const { return sig; }
 
diff --git a/src/testlib/qsignalspy.qdoc b/src/testlib/qsignalspy.qdoc
index 3352307d69..5ea6bc5dc7 100644
--- a/src/testlib/qsignalspy.qdoc
+++ b/src/testlib/qsignalspy.qdoc
@@ -86,6 +86,28 @@
     \snippet code/doc_src_qsignalspy.cpp 6
 */
 
+/*! \fn QSignalSpy(const QObject *obj, const QMetaMethod &signal)
+    \since 5.14
+
+    Constructs a new QSignalSpy that listens for emissions of the \a signal
+    from the QObject \a object. If QSignalSpy is not able to listen for a
+    valid signal (for example, because \a object is \nullptr or \a signal does
+    not denote a valid signal of \a object), an explanatory warning message
+    will be output using qWarning() and subsequent calls to \c isValid() will
+    return false.
+
+    This constructor is convenient to use when Qt's meta-object system is
+    heavily used in a test.
+
+    Basic usage example:
+    \snippet code/doc_src_qsignalspy.cpp 7
+
+    Imagine we need to check whether all properties of the QWindow class
+    that represent minimum and maximum dimensions are properly writable.
+    The following example demonstrates one of the approaches:
+    \snippet code/doc_src_qsignalspy.cpp 8
+*/
+
 /*! \fn QSignalSpy::isValid() const
 
     Returns \c true if the signal spy listens to a valid signal, otherwise false.