QLatin1String: add test

QLatin1String wasn't really tested except as a drive-by.
Unearthed a discrepancy with docs. Fixed the docs.

Change-Id: I1246bb33888132edbc4e22da792a480a156357bf
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>

src/corelib/tools/qstring.cpp

@@ -8227,9 +8227,7 @@ QString &QString::setRawData(const QChar *unicode, int size)
 
 /*! \fn QLatin1String::QLatin1String(const char *str)
 
-    Constructs a QLatin1String object that stores \a str. Note that if
+    Constructs a QLatin1String object that stores \a str.
-    \a str is 0, an empty string is created; this case is handled by
-    QString.
 
     The string data is \e not copied. The caller must be able to
     guarantee that \a str will not be deleted or modified as long as
@@ -8241,8 +8239,6 @@ QString &QString::setRawData(const QChar *unicode, int size)
 /*! \fn QLatin1String::QLatin1String(const char *str, int size)
 
     Constructs a QLatin1String object that stores \a str with \a size.
-    Note that if \a str is 0, an empty string is created; this case
-    is handled by QString.
 
     The string data is \e not copied. The caller must be able to
     guarantee that \a str will not be deleted or modified as long as

tests/auto/corelib/tools/qlatin1string/.gitignore

@@ -0,0 +1 @@
+tst_qlatin1string

tests/auto/corelib/tools/qlatin1string/qlatin1string.pro

@@ -0,0 +1,8 @@
+CONFIG += testcase parallel_test
+TARGET = tst_qlatin1string
+QT = core testlib
+SOURCES = tst_qlatin1string.cpp
+DEFINES += QT_NO_CAST_TO_ASCII
+contains(QT_CONFIG,c++11): CONFIG += c++11 c++14
+
+DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0

tests/auto/corelib/tools/qlatin1string/tst_qlatin1string.cpp

@@ -0,0 +1,116 @@
+/****************************************************************************
+**
+** Copyright (C) 2015 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Marc Mutz <marc.mutz@kdab.com>
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL21$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 or version 3 as published by the Free
+** Software Foundation and appearing in the file LICENSE.LGPLv21 and
+** LICENSE.LGPLv3 included in the packaging of this file. Please review the
+** following information to ensure the GNU Lesser General Public License
+** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** As a special exception, The Qt Company gives you certain additional
+** rights. These rights are described in The Qt Company LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtTest/QtTest>
+
+#include <QString>
+
+class tst_QLatin1String : public QObject
+{
+    Q_OBJECT
+
+private Q_SLOTS:
+    void nullString();
+    void emptyString();
+};
+
+void tst_QLatin1String::nullString()
+{
+    // from nullptr
+    {
+        const char *null = Q_NULLPTR;
+        QLatin1String l1(null);
+        QCOMPARE(static_cast<const void*>(l1.data()), static_cast<const void*>(Q_NULLPTR));
+        QCOMPARE(l1.size(), 0);
+
+        QString s = l1;
+        QVERIFY(s.isNull());
+    }
+
+    // from null QByteArray
+    {
+        const QByteArray null;
+        QVERIFY(null.isNull());
+
+        QLatin1String l1(null);
+        QEXPECT_FAIL("", "null QByteArrays become non-null QLatin1Strings...", Continue);
+        QCOMPARE(static_cast<const void*>(l1.data()), static_cast<const void*>(Q_NULLPTR));
+        QCOMPARE(l1.size(), 0);
+
+        QString s = l1;
+        QEXPECT_FAIL("", "null QByteArrays become non-null QLatin1Strings become non-null QStrings...", Continue);
+        QVERIFY(s.isNull());
+    }
+}
+
+void tst_QLatin1String::emptyString()
+{
+    {
+        const char *empty = "";
+        QLatin1String l1(empty);
+        QCOMPARE(static_cast<const void*>(l1.data()), static_cast<const void*>(empty));
+        QCOMPARE(l1.size(), 0);
+
+        QString s = l1;
+        QVERIFY(s.isEmpty());
+        QVERIFY(!s.isNull());
+    }
+
+    {
+        const char *notEmpty = "foo";
+        QLatin1String l1(notEmpty, 0);
+        QCOMPARE(static_cast<const void*>(l1.data()), static_cast<const void*>(notEmpty));
+        QCOMPARE(l1.size(), 0);
+
+        QString s = l1;
+        QVERIFY(s.isEmpty());
+        QVERIFY(!s.isNull());
+    }
+
+    {
+        const QByteArray empty = "";
+        QLatin1String l1(empty);
+        QCOMPARE(static_cast<const void*>(l1.data()), static_cast<const void*>(empty.constData()));
+        QCOMPARE(l1.size(), 0);
+
+        QString s = l1;
+        QVERIFY(s.isEmpty());
+        QVERIFY(!s.isNull());
+    }
+}
+
+
+
+QTEST_APPLESS_MAIN(tst_QLatin1String)
+
+#include "tst_qlatin1string.moc"

tests/auto/corelib/tools/tools.pro

@@ -24,6 +24,7 @@ SUBDIRS=\
     qhash \
     qhash_strictiterators \
     qhashfunctions \
+    qlatin1string \
     qline \
     qlinkedlist \
     qlist \