diff --git a/src/testlib/qabstracttestlogger_p.h b/src/testlib/qabstracttestlogger_p.h
index 9bb1d1e80c..e5a1404c16 100644
--- a/src/testlib/qabstracttestlogger_p.h
+++ b/src/testlib/qabstracttestlogger_p.h
@@ -117,8 +117,7 @@ struct QTestCharBuffer
 {
     enum { InitialSize = 512 };
 
-    inline QTestCharBuffer()
-            : _size(InitialSize), buf(staticBuf)
+    inline QTestCharBuffer() : buf(staticBuf)
     {
         staticBuf[0] = '\0';
     }
@@ -170,7 +169,7 @@ struct QTestCharBuffer
     }
 
 private:
-    int _size;
+    int _size = InitialSize;
     char* buf;
     char staticBuf[InitialSize];
 };
diff --git a/src/testlib/qbenchmark.cpp b/src/testlib/qbenchmark.cpp
index cbc009c993..19abd16284 100644
--- a/src/testlib/qbenchmark.cpp
+++ b/src/testlib/qbenchmark.cpp
@@ -51,14 +51,6 @@ QT_BEGIN_NAMESPACE
 QBenchmarkGlobalData *QBenchmarkGlobalData::current;
 
 QBenchmarkGlobalData::QBenchmarkGlobalData()
-    : measurer(0)
-    , walltimeMinimum(-1)
-    , iterationCount(-1)
-    , medianIterationCount(-1)
-    , createChart(false)
-    , verboseOutput(false)
-    , minimumTotal(-1)
-    , mode_(WallTime)
 {
     setMode(mode_);
 }
@@ -116,10 +108,7 @@ int QBenchmarkGlobalData::adjustMedianIterationCount()
 
 QBenchmarkTestMethodData *QBenchmarkTestMethodData::current;
 
-QBenchmarkTestMethodData::QBenchmarkTestMethodData()
-:resultAccepted(false), runOnce(false), iterationCount(-1)
-{
-}
+QBenchmarkTestMethodData::QBenchmarkTestMethodData() = default;
 
 QBenchmarkTestMethodData::~QBenchmarkTestMethodData()
 {
diff --git a/src/testlib/qbenchmark_p.h b/src/testlib/qbenchmark_p.h
index 49868ac23a..93b5becb2b 100644
--- a/src/testlib/qbenchmark_p.h
+++ b/src/testlib/qbenchmark_p.h
@@ -81,7 +81,7 @@ struct QBenchmarkContext
     QString slotName;
     QString tag; // from _data() function
 
-    int checkpointIndex;
+    int checkpointIndex = -1;
 
     QString toString() const
     {
@@ -89,7 +89,7 @@ struct QBenchmarkContext
                .arg(slotName, tag, QString::number(checkpointIndex));
     }
 
-    QBenchmarkContext() : checkpointIndex(-1) {}
+    QBenchmarkContext()  = default;
 };
 Q_DECLARE_TYPEINFO(QBenchmarkContext, Q_MOVABLE_TYPE);
 
@@ -97,19 +97,13 @@ class QBenchmarkResult
 {
 public:
     QBenchmarkContext context;
-    qreal value;
-    int iterations;
-    QTest::QBenchmarkMetric metric;
-    bool setByMacro;
-    bool valid;
+    qreal value = -1;
+    int iterations = -1;
+    QTest::QBenchmarkMetric metric = QTest::FramesPerSecond;
+    bool setByMacro = true;
+    bool valid = false;
 
-    QBenchmarkResult()
-    : value(-1)
-    , iterations(-1)
-    , metric(QTest::FramesPerSecond)
-    , setByMacro(true)
-    , valid(false)
-    { }
+    QBenchmarkResult() = default;
 
     QBenchmarkResult(
         const QBenchmarkContext &context, const qreal value, const int iterations,
@@ -147,17 +141,17 @@ public:
     QBenchmarkMeasurerBase *createMeasurer();
     int adjustMedianIterationCount();
 
-    QBenchmarkMeasurerBase *measurer;
+    QBenchmarkMeasurerBase *measurer = nullptr;
     QBenchmarkContext context;
-    int walltimeMinimum;
-    int iterationCount;
-    int medianIterationCount;
-    bool createChart;
-    bool verboseOutput;
+    int walltimeMinimum = -1;
+    int iterationCount = -1;
+    int medianIterationCount = -1;
+    bool createChart = false;
+    bool verboseOutput = false;
     QString callgrindOutFileBase;
-    int minimumTotal;
+    int minimumTotal = -1;
 private:
-    Mode mode_;
+    Mode mode_ = WallTime;
 };
 
 /*
@@ -184,9 +178,9 @@ public:
     void setResult(qreal value, QTest::QBenchmarkMetric metric, bool setByMacro = true);
 
     QBenchmarkResult result;
-    bool resultAccepted;
-    bool runOnce;
-    int iterationCount;
+    bool resultAccepted = false;
+    bool runOnce = false;
+    int iterationCount = -1;
 };
 
 // low-level API:
diff --git a/src/testlib/qbenchmarkevent.cpp b/src/testlib/qbenchmarkevent.cpp
index a8270219e4..41be9fa468 100644
--- a/src/testlib/qbenchmarkevent.cpp
+++ b/src/testlib/qbenchmarkevent.cpp
@@ -44,10 +44,7 @@
 
 QT_BEGIN_NAMESPACE
 
-QBenchmarkEvent::QBenchmarkEvent()
-    : eventCounter(0)
-{
-}
+QBenchmarkEvent::QBenchmarkEvent() = default;
 
 QBenchmarkEvent::~QBenchmarkEvent()
 {
diff --git a/src/testlib/qbenchmarkevent_p.h b/src/testlib/qbenchmarkevent_p.h
index 0f47aa475c..9fe3daa33b 100644
--- a/src/testlib/qbenchmarkevent_p.h
+++ b/src/testlib/qbenchmarkevent_p.h
@@ -76,7 +76,7 @@ public:
 #else
     bool nativeEventFilter(const QByteArray &eventType, void *message, long *result) override;
 #endif
-    qint64 eventCounter;
+    qint64 eventCounter = 0;
 };
 
 QT_END_NAMESPACE
diff --git a/src/testlib/qbenchmarkperfevents.cpp b/src/testlib/qbenchmarkperfevents.cpp
index 91f0792338..ea27f29711 100644
--- a/src/testlib/qbenchmarkperfevents.cpp
+++ b/src/testlib/qbenchmarkperfevents.cpp
@@ -500,10 +500,7 @@ void QBenchmarkPerfEventsMeasurer::listCounters()
            "Attributes can be combined, for example: -perfcounter branch-mispredicts:kh\n");
 }
 
-QBenchmarkPerfEventsMeasurer::QBenchmarkPerfEventsMeasurer()
-    : fd(-1)
-{
-}
+QBenchmarkPerfEventsMeasurer::QBenchmarkPerfEventsMeasurer() = default;
 
 QBenchmarkPerfEventsMeasurer::~QBenchmarkPerfEventsMeasurer()
 {
diff --git a/src/testlib/qbenchmarkperfevents_p.h b/src/testlib/qbenchmarkperfevents_p.h
index 86ba556549..47af4db9f8 100644
--- a/src/testlib/qbenchmarkperfevents_p.h
+++ b/src/testlib/qbenchmarkperfevents_p.h
@@ -76,7 +76,7 @@ public:
     static void setCounter(const char *name);
     static void listCounters();
 private:
-    int fd;
+    int fd = -1;
 
     qint64 readValue();
 };
diff --git a/src/testlib/qtestcoreelement_p.h b/src/testlib/qtestcoreelement_p.h
index 84406fed85..a101ab5ea3 100644
--- a/src/testlib/qtestcoreelement_p.h
+++ b/src/testlib/qtestcoreelement_p.h
@@ -74,13 +74,13 @@ class QTestCoreElement: public QTestCoreList<ElementType>
         QTest::LogElementType elementType() const;
 
     private:
-        QTestElementAttribute *listOfAttributes;
+        QTestElementAttribute *listOfAttributes = nullptr;
         QTest::LogElementType type;
 };
 
 template<class ElementType>
 QTestCoreElement<ElementType>::QTestCoreElement(int t)
-    :listOfAttributes(nullptr), type(QTest::LogElementType(t))
+    : type(QTest::LogElementType(t))
 {
 }
 
diff --git a/src/testlib/qtestdata.cpp b/src/testlib/qtestdata.cpp
index a8ee130a7d..3a1c6d7e7b 100644
--- a/src/testlib/qtestdata.cpp
+++ b/src/testlib/qtestdata.cpp
@@ -51,12 +51,10 @@ QT_BEGIN_NAMESPACE
 class QTestDataPrivate
 {
 public:
-    QTestDataPrivate() : tag(0), parent(0), data(0), dataCount(0) {}
-
-    char *tag;
-    QTestTable *parent;
-    void **data;
-    int dataCount;
+    char *tag = nullptr;
+    QTestTable *parent = nullptr;
+    void **data = nullptr;
+    int dataCount = 0;
 };
 
 QTestData::QTestData(const char *tag, QTestTable *parent)
diff --git a/src/testlib/qtestelement.cpp b/src/testlib/qtestelement.cpp
index 622e5344f3..b468295917 100644
--- a/src/testlib/qtestelement.cpp
+++ b/src/testlib/qtestelement.cpp
@@ -43,8 +43,6 @@ QT_BEGIN_NAMESPACE
 
 QTestElement::QTestElement(int type)
     : QTestCoreElement<QTestElement>(type)
-    , listOfChildren(0)
-    , parent(0)
 {
 }
 
diff --git a/src/testlib/qtestelement_p.h b/src/testlib/qtestelement_p.h
index dacbe6c106..a6b2791a42 100644
--- a/src/testlib/qtestelement_p.h
+++ b/src/testlib/qtestelement_p.h
@@ -69,8 +69,8 @@ class QTestElement: public QTestCoreElement<QTestElement>
         void setParent(const QTestElement *p);
 
     private:
-        QTestElement *listOfChildren;
-        const QTestElement * parent;
+        QTestElement *listOfChildren = nullptr;
+        const QTestElement * parent = nullptr;
 
 };
 
diff --git a/src/testlib/qtestelementattribute.cpp b/src/testlib/qtestelementattribute.cpp
index 9d752bf26a..1aa54d767f 100644
--- a/src/testlib/qtestelementattribute.cpp
+++ b/src/testlib/qtestelementattribute.cpp
@@ -104,11 +104,7 @@ QT_BEGIN_NAMESPACE
   \value LET_SystemError
 */
 
-QTestElementAttribute::QTestElementAttribute()
-    :attributeValue(0),
-    attributeIndex(QTest::AI_Undefined)
-{
-}
+QTestElementAttribute::QTestElementAttribute() = default;
 
 QTestElementAttribute::~QTestElementAttribute()
 {
diff --git a/src/testlib/qtestelementattribute_p.h b/src/testlib/qtestelementattribute_p.h
index cb4dbb5f16..f3815b72d1 100644
--- a/src/testlib/qtestelementattribute_p.h
+++ b/src/testlib/qtestelementattribute_p.h
@@ -106,8 +106,8 @@ class QTestElementAttribute: public QTestCoreList<QTestElementAttribute>
         bool setPair(QTest::AttributeIndex attributeIndex, const char *value);
 
     private:
-        char *attributeValue;
-        QTest::AttributeIndex attributeIndex;
+        char *attributeValue = nullptr;
+        QTest::AttributeIndex attributeIndex = QTest::AI_Undefined;
 };
 
 QT_END_NAMESPACE
diff --git a/src/testlib/qtesteventloop.h b/src/testlib/qtesteventloop.h
index a77b47cd7f..b194e24c3a 100644
--- a/src/testlib/qtesteventloop.h
+++ b/src/testlib/qtesteventloop.h
@@ -56,8 +56,7 @@ class Q_TESTLIB_EXPORT QTestEventLoop : public QObject
     Q_OBJECT
 
 public:
-    inline QTestEventLoop(QObject *aParent = nullptr)
-        : QObject(aParent), inLoop(false), _timeout(false), timerId(-1), loop(nullptr) {}
+    using QObject::QObject;
 
     inline void enterLoopMSecs(int ms);
     inline void enterLoop(int secs) { enterLoopMSecs(secs * 1000); }
@@ -84,10 +83,10 @@ protected:
 
 private:
     Q_DECL_UNUSED_MEMBER bool inLoop; // ### Qt 6: remove
-    bool _timeout;
-    int timerId;
+    bool _timeout = false;
+    int timerId = -1;
 
-    QEventLoop *loop;
+    QEventLoop *loop = nullptr;
 };
 
 inline void QTestEventLoop::enterLoopMSecs(int ms)
diff --git a/src/testlib/qtestlog.cpp b/src/testlib/qtestlog.cpp
index 14543c3cde..ddebf1105f 100644
--- a/src/testlib/qtestlog.cpp
+++ b/src/testlib/qtestlog.cpp
@@ -111,7 +111,7 @@ namespace QTest {
     struct IgnoreResultList
     {
         inline IgnoreResultList(QtMsgType tp, const QVariant &patternIn)
-            : type(tp), pattern(patternIn), next(0) {}
+            : type(tp), pattern(patternIn) {}
 
         static inline void clearList(IgnoreResultList *&list)
         {
@@ -163,7 +163,7 @@ namespace QTest {
 
         QtMsgType type;
         QVariant pattern;
-        IgnoreResultList *next;
+        IgnoreResultList *next = nullptr;
     };
 
     static IgnoreResultList *ignoreResultList = 0;
diff --git a/src/testlib/qtesttable.cpp b/src/testlib/qtesttable.cpp
index 20e0702d44..e2e72b125f 100644
--- a/src/testlib/qtesttable.cpp
+++ b/src/testlib/qtesttable.cpp
@@ -58,11 +58,11 @@ public:
     }
 
     struct Element {
-        Element() : name(nullptr), type(0) {}
+        Element() = default;
         Element(const char *n, int t) : name(n), type(t) {}
 
-        const char *name;
-        int type;
+        const char *name = nullptr;
+        int type = 0;
     };
 
     using ElementList = std::vector<Element>;
diff --git a/src/testlib/qxunittestlogger.cpp b/src/testlib/qxunittestlogger.cpp
index 336edb5994..cae959a349 100644
--- a/src/testlib/qxunittestlogger.cpp
+++ b/src/testlib/qxunittestlogger.cpp
@@ -59,13 +59,6 @@ QT_BEGIN_NAMESPACE
 
 QXunitTestLogger::QXunitTestLogger(const char *filename)
     : QAbstractTestLogger(filename)
-    , listOfTestcases(0)
-    , currentLogElement(0)
-    , errorLogElement(0)
-    , logFormatter(0)
-    , testCounter(0)
-    , failureCounter(0)
-    , errorCounter(0)
 {
 }
 
diff --git a/src/testlib/qxunittestlogger_p.h b/src/testlib/qxunittestlogger_p.h
index 48f07ddcf2..518ba098f4 100644
--- a/src/testlib/qxunittestlogger_p.h
+++ b/src/testlib/qxunittestlogger_p.h
@@ -79,14 +79,14 @@ class QXunitTestLogger : public QAbstractTestLogger
                     const char *file = nullptr, int line = 0) override;
 
     private:
-        QTestElement *listOfTestcases;
-        QTestElement *currentLogElement;
-        QTestElement *errorLogElement;
-        QTestXunitStreamer *logFormatter;
+        QTestElement *listOfTestcases = nullptr;
+        QTestElement *currentLogElement = nullptr;
+        QTestElement *errorLogElement = nullptr;
+        QTestXunitStreamer *logFormatter = nullptr;
 
-        int testCounter;
-        int failureCounter;
-        int errorCounter;
+        int testCounter = 0;
+        int failureCounter = 0;
+        int errorCounter = 0;
 };
 
 QT_END_NAMESPACE