diff --git a/src/libcalamares/packages/Tests.cpp b/src/libcalamares/packages/Tests.cpp
index 0a9be3a20..09159abdf 100644
--- a/src/libcalamares/packages/Tests.cpp
+++ b/src/libcalamares/packages/Tests.cpp
@@ -24,7 +24,15 @@ private Q_SLOTS:
     void initTestCase();
 
     void testEmpty();
+    void testAdd_data();
+    /** @brief Test various add calls, for a "clean" GS
+     *
+     * Check that adding through the variant- and the stringlist-API
+     * does the same thing.
+     */
     void testAdd();
+    /// Test replacement and mixing string-list with variant calls
+    void testAddMixed();
 };
 
 void
@@ -46,38 +54,179 @@ PackagesTests::testEmpty()
     // Adding nothing at all does nothing
     QVERIFY( !CalamaresUtils::Packages::setGSPackageAdditions( &gs, k, QVariantList(), QVariantList() ) );
     QVERIFY( !gs.contains( topKey ) );
+
+    QVERIFY( !CalamaresUtils::Packages::setGSPackageAdditions( &gs, k, QStringList() ) );
+    QVERIFY( !gs.contains( topKey ) );
+}
+
+void
+PackagesTests::testAdd_data()
+{
+    QTest::addColumn< QStringList >( "packages" );
+
+    QTest::newRow( "one" ) << QStringList { QString( "vim" ) };
+    QTest::newRow( "two" ) << QStringList { QString( "vim" ), QString( "emacs" ) };
+    QTest::newRow( "one-again" ) << QStringList { QString( "nano" ) };
+    QTest::newRow( "six" ) << QStringList { QString( "vim" ),  QString( "emacs" ), QString( "nano" ),
+                                            QString( "kate" ), QString( "gedit" ), QString( "sublime" ) };
+    // There is no "de-duplication" so this will insert "cim" twice
+    QTest::newRow( "dups" ) << QStringList { QString( "cim" ), QString( "vim" ), QString( "cim" ) };
 }
 
 void
 PackagesTests::testAdd()
 {
     Calamares::GlobalStorage gs;
+
+    const QString extraEditor( "notepad++" );
     const QString topKey( "packageOperations" );
     Calamares::ModuleSystem::InstanceKey k( "this", "that" );
+    Calamares::ModuleSystem::InstanceKey otherInstance( "this", "other" );
 
-    QVERIFY( !gs.contains( topKey ) );
-    QVERIFY(
-        CalamaresUtils::Packages::setGSPackageAdditions( &gs, k, QVariantList { QString( "vim" ) }, QVariantList() ) );
-    QVERIFY( gs.contains( topKey ) );
-    auto actionList = gs.value( topKey ).toList();
-    QCOMPARE( actionList.length(), 1 );
-    auto action = actionList[ 0 ].toMap();
-    QVERIFY( action.contains( "install" ) );
-    auto op = action[ "install" ].toList();
-    QCOMPARE( op.length(), 1 );
-    cDebug() << op;
+    QFETCH( QStringList, packages );
+    QVERIFY( !packages.contains( extraEditor ) );
 
-    QVERIFY( CalamaresUtils::Packages::setGSPackageAdditions(
-        &gs, k, QVariantList { QString( "vim" ), QString( "emacs" ) }, QVariantList() ) );
-    QVERIFY( gs.contains( topKey ) );
-    actionList = gs.value( topKey ).toList();
-    QCOMPARE( actionList.length(), 1 );
-    action = actionList[ 0 ].toMap();
-    QVERIFY( action.contains( "install" ) );
-    op = action[ "install" ].toList();
-    QCOMPARE( op.length(), 2 );
-    QCOMPARE( action[ "source" ].toString(), k.toString() );
-    cDebug() << op;
+    {
+        QVERIFY( !gs.contains( topKey ) );
+        QVERIFY(
+            CalamaresUtils::Packages::setGSPackageAdditions( &gs, k, QVariant( packages ).toList(), QVariantList() ) );
+        QVERIFY( gs.contains( topKey ) );
+        auto actionList = gs.value( topKey ).toList();
+        QCOMPARE( actionList.length(), 1 );
+        auto action = actionList[ 0 ].toMap();
+        QVERIFY( action.contains( "install" ) );
+        auto op = action[ "install" ].toList();
+        QCOMPARE( op.length(), packages.length() );
+        for ( const auto& s : qAsConst( packages ) )
+        {
+            QVERIFY( op.contains( s ) );
+        }
+        cDebug() << op;
+    }
+    {
+        QVERIFY( CalamaresUtils::Packages::setGSPackageAdditions( &gs, otherInstance, packages ) );
+        QVERIFY( gs.contains( topKey ) );
+        auto actionList = gs.value( topKey ).toList();
+        QCOMPARE( actionList.length(), 2 );  // One for each instance key!
+        auto action = actionList[ 0 ].toMap();
+        auto secondaction = actionList[ 1 ].toMap();
+        auto op = action[ "install" ].toList();
+        auto secondop = secondaction[ "install" ].toList();
+        QCOMPARE( op, secondop );
+    }
+
+    {
+        // Replace one and expect differences
+        packages << extraEditor;
+        QVERIFY( CalamaresUtils::Packages::setGSPackageAdditions( &gs, otherInstance, packages ) );
+        QVERIFY( gs.contains( topKey ) );
+        auto actionList = gs.value( topKey ).toList();
+        QCOMPARE( actionList.length(), 2 );  // One for each instance key!
+        for ( const auto& actionVariant : qAsConst( actionList ) )
+        {
+            auto action = actionVariant.toMap();
+            QVERIFY( action.contains( "install" ) );
+            QVERIFY( action.contains( "source" ) );
+            if ( action[ "source" ].toString() == otherInstance.toString() )
+            {
+                auto op = action[ "install" ].toList();
+                QCOMPARE( op.length(), packages.length() );  // changed from original length, though
+                for ( const auto& s : qAsConst( packages ) )
+                {
+                    QVERIFY( op.contains( s ) );
+                }
+            }
+            else
+            {
+                // This is the "original" instance, so it's missing extraEditor
+                auto op = action[ "install" ].toList();
+                QCOMPARE( op.length(), packages.length()-1 );  // changed from original length
+                QVERIFY( !op.contains( extraEditor ) );
+            }
+        }
+    }
+}
+
+void
+PackagesTests::testAddMixed()
+{
+    Calamares::GlobalStorage gs;
+
+    const QString extraEditor( "notepad++" );
+    const QString topKey( "packageOperations" );
+    Calamares::ModuleSystem::InstanceKey k( "this", "that" );
+    Calamares::ModuleSystem::InstanceKey otherInstance( "this", "other" );
+
+    // Just one
+    {
+        QVERIFY( !gs.contains( topKey ) );
+        QVERIFY( CalamaresUtils::Packages::setGSPackageAdditions(
+            &gs, k, QVariantList { QString( "vim" ) }, QVariantList() ) );
+        QVERIFY( gs.contains( topKey ) );
+        auto actionList = gs.value( topKey ).toList();
+        QCOMPARE( actionList.length(), 1 );
+        auto action = actionList[ 0 ].toMap();
+        QVERIFY( action.contains( "install" ) );
+        auto op = action[ "install" ].toList();
+        QCOMPARE( op.length(), 1 );
+        QCOMPARE( op[ 0 ], QString( "vim" ) );
+        cDebug() << op;
+    }
+
+    // Replace with two packages
+    {
+        QVERIFY( CalamaresUtils::Packages::setGSPackageAdditions(
+            &gs, k, QVariantList { QString( "vim" ), QString( "emacs" ) }, QVariantList() ) );
+        QVERIFY( gs.contains( topKey ) );
+        auto actionList = gs.value( topKey ).toList();
+        QCOMPARE( actionList.length(), 1 );
+        auto action = actionList[ 0 ].toMap();
+        QVERIFY( action.contains( "install" ) );
+        auto op = action[ "install" ].toList();
+        QCOMPARE( op.length(), 2 );
+        QCOMPARE( action[ "source" ].toString(), k.toString() );
+        QVERIFY( op.contains( QString( "vim" ) ) );
+        QVERIFY( op.contains( QString( "emacs" ) ) );
+        cDebug() << op;
+    }
+
+    // Replace with one (different) package
+    {
+        QVERIFY( CalamaresUtils::Packages::setGSPackageAdditions(
+            &gs, k, QVariantList { QString( "nano" ) }, QVariantList() ) );
+        QVERIFY( gs.contains( topKey ) );
+        auto actionList = gs.value( topKey ).toList();
+        QCOMPARE( actionList.length(), 1 );
+        auto action = actionList[ 0 ].toMap();
+        QVERIFY( action.contains( "install" ) );
+        auto op = action[ "install" ].toList();
+        QCOMPARE( op.length(), 1 );
+        QCOMPARE( action[ "source" ].toString(), k.toString() );
+        QCOMPARE( op[ 0 ], QString( "nano" ) );
+        cDebug() << op;
+    }
+
+    // Now we have two sources
+    {
+        QVERIFY( CalamaresUtils::Packages::setGSPackageAdditions( &gs, otherInstance, QStringList( extraEditor ) ) );
+        QVERIFY( gs.contains( topKey ) );
+        auto actionList = gs.value( topKey ).toList();
+        QCOMPARE( actionList.length(), 2 );
+
+        for ( const auto& actionVariant : qAsConst( actionList ) )
+        {
+            auto action = actionVariant.toMap();
+            QVERIFY( action.contains( "install" ) );
+            QVERIFY( action.contains( "source" ) );
+            if ( action[ "source" ].toString() == otherInstance.toString() )
+            {
+                auto op = action[ "install" ].toList();
+                QCOMPARE( op.length(), 1 );
+                QVERIFY(
+                    op.contains( action[ "source" ] == otherInstance.toString() ? extraEditor : QString( "nano" ) ) );
+            }
+        }
+    }
 }