diff --git a/autotests/CMakeLists.txt b/autotests/CMakeLists.txt
--- a/autotests/CMakeLists.txt
+++ b/autotests/CMakeLists.txt
@@ -18,7 +18,7 @@
 # KSldTest
 #######################################
 add_executable(ksldTest ksldtest.cpp)
-target_link_libraries(ksldTest Qt5::Test KScreenLocker)
+target_link_libraries(ksldTest Qt5::Test Qt5::Widgets KF5::IdleTime KScreenLocker)
 add_test(ksmserver-ksldTest ksldTest)
 ecm_mark_as_test(ksldTest)
 
diff --git a/autotests/ksldtest.cpp b/autotests/ksldtest.cpp
--- a/autotests/ksldtest.cpp
+++ b/autotests/ksldtest.cpp
@@ -19,6 +19,8 @@
 *********************************************************************/
 // own
 #include "../ksldapp.h"
+// KDE Frameworks
+#include <KIdleTime>
 // Qt
 #include <QtTest/QtTest>
 #include <QProcess>
@@ -31,6 +33,7 @@
 private Q_SLOTS:
     void initTestCase();
     void testEstablishGrab();
+    void testActivateOnTimeout();
 };
 
 void KSldTest::initTestCase()
@@ -89,5 +92,37 @@
     QVERIFY(ksld.establishGrab());
 }
 
+void KSldTest::testActivateOnTimeout()
+{
+    // this time verifies that the screen gets locked on idle timeout, requires the system to be idle
+    ScreenLocker::KSldApp ksld;
+    ksld.initialize();
+
+    // we need to modify the idle timeout of KSLD, it's in minutes we cannot wait that long
+    if (ksld.idleId() != 0) {
+        // remove old Idle id
+        KIdleTime::instance()->removeIdleTimeout(ksld.idleId());
+    }
+    ksld.setIdleId(KIdleTime::instance()->addIdleTimeout(5000));
+
+    QSignalSpy lockStateChangedSpy(&ksld, &ScreenLocker::KSldApp::lockStateChanged);
+    QVERIFY(lockStateChangedSpy.isValid());
+
+    // let's wait the double of the idle timeout
+    QVERIFY(lockStateChangedSpy.wait(10000));
+    QCOMPARE(ksld.lockState(), ScreenLocker::KSldApp::AcquiringLock);
+
+    // let's simulate unlock to get rid of started greeter process
+    const auto children = ksld.children();
+    for (auto it = children.begin(); it != children.end(); ++it) {
+        if (qstrcmp((*it)->metaObject()->className(), "LogindIntegration") != 0) {
+            continue;
+        }
+        QMetaObject::invokeMethod(*it, "requestUnlock");
+        break;
+    }
+    QVERIFY(lockStateChangedSpy.wait());
+}
+
 QTEST_MAIN(KSldTest)
 #include "ksldtest.moc"
diff --git a/ksldapp.h b/ksldapp.h
--- a/ksldapp.h
+++ b/ksldapp.h
@@ -104,6 +104,21 @@
 
     bool event(QEvent *event) override;
 
+    /**
+     * For testing
+     * @internal
+     **/
+    int idleId() const {
+        return m_idleId;
+    }
+    /**
+     * For testing
+     * @internal
+     **/
+    void setIdleId(int idleId) {
+        m_idleId = idleId;
+    }
+
 Q_SIGNALS:
     void locked();
     void unlocked();