diff --git a/smb/CMakeLists.txt b/smb/CMakeLists.txt
--- a/smb/CMakeLists.txt
+++ b/smb/CMakeLists.txt
@@ -73,3 +73,5 @@
 install(TARGETS kio_smb DESTINATION ${KDE_INSTALL_PLUGINDIR}/kf5/kio)
 install(FILES smb-network.desktop DESTINATION ${KDE_INSTALL_DATADIR}/konqueror/dirtree/remote)
 install(FILES smb-network.desktop DESTINATION ${KDE_INSTALL_DATADIR}/remoteview)
+
+add_subdirectory(autotests)
diff --git a/smb/autotests/CMakeLists.txt b/smb/autotests/CMakeLists.txt
new file mode 100644
--- /dev/null
+++ b/smb/autotests/CMakeLists.txt
@@ -0,0 +1,17 @@
+if(NOT BUILD_TESTING)
+    return()
+endif()
+
+# allow coercing cstring to qstring, easier to write
+remove_definitions(-DQT_NO_CAST_FROM_ASCII)
+
+find_package(Qt5Test ${QT_MIN_VERSION} CONFIG REQUIRED)
+
+include(ECMAddTests)
+
+ecm_add_tests(
+    smburltest
+    LINK_LIBRARIES
+        Qt5::Test
+        kio_smb_static
+)
diff --git a/smb/autotests/smburltest.cpp b/smb/autotests/smburltest.cpp
new file mode 100644
--- /dev/null
+++ b/smb/autotests/smburltest.cpp
@@ -0,0 +1,69 @@
+/*
+    SPDX-FileCopyrightText: 2020 Harald Sitter <sitter@kde.org>
+    SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+*/
+
+#include <QTest>
+#include <QAbstractItemModelTester>
+
+#include "smburl.h"
+
+class SMBUrlTest : public QObject
+{
+    Q_OBJECT
+private Q_SLOTS:
+    void testMinimalToSmbcValid()
+    {
+        // libsmbclient is a bit picky. make sure we convert to minimal applicable form
+        {
+            SMBUrl url(QUrl("smb:/"));
+            QCOMPARE(url.toSmbcUrl(), "smb://");
+        }
+
+        // But at the same time it will happily deal with smb:
+        {
+            SMBUrl url(QUrl("smb:"));
+            QCOMPARE(url.toSmbcUrl(), "smb:");
+        }
+    }
+
+    void testType()
+    {
+        QCOMPARE(SMBUrl(QUrl("smb://")).getType(), SMBURLTYPE_ENTIRE_NETWORK);
+        QCOMPARE(SMBUrl(QUrl("smb://host")).getType(), SMBURLTYPE_WORKGROUP_OR_SERVER);
+        QCOMPARE(SMBUrl(QUrl("smb://host/share/file")).getType(), SMBURLTYPE_SHARE_OR_PATH);
+        QCOMPARE(SMBUrl(QUrl()).getType(), SMBURLTYPE_UNKNOWN);
+    }
+
+    void testPart()
+    {
+        SMBUrl url(QUrl("smb://host/share/file"));
+        QCOMPARE(url.partUrl().toString(), "smb://host/share/file.part");
+    }
+
+    void testUp()
+    {
+        SMBUrl url(QUrl("smb://host/share/file"));
+        url.cd("..");
+        QCOMPARE(url.toSmbcUrl(), "smb://host/share");
+    }
+
+    void testAddPath()
+    {
+        SMBUrl url(QUrl("smb://host/share"));
+        url.addPath("file");
+        QCOMPARE(url.toSmbcUrl(), "smb://host/share/file");
+    }
+
+    void testCifs()
+    {
+        // We treat cifs as an alias but need to translate it to smb.
+        // https://bugs.kde.org/show_bug.cgi?id=327295
+        SMBUrl url(QUrl("cifs://host/share/file"));
+        QCOMPARE(url.toSmbcUrl(), "smb://host/share/file");
+    }
+};
+
+QTEST_GUILESS_MAIN(SMBUrlTest)
+
+#include "smburltest.moc"
diff --git a/smb/smburl.cpp b/smb/smburl.cpp
--- a/smb/smburl.cpp
+++ b/smb/smburl.cpp
@@ -69,7 +69,9 @@
     if (filedir == "..") {
         setUrl(KIO::upUrl(*this).url());
     } else {
-        setUrl(filedir);
+        // We only support going up right now! It's all we need doing!
+        Q_UNREACHABLE();
+        return false;
     }
     updateCache();
     return true;