[Tests] Use QtTest for model contracts and signal spies (#7630)

Qt6::Test was linked into every test but never used. Add a small RAII
QAbstractItemModelTester helper and apply it to the deck list model, the card
database model and display proxy, and the sets model. Add QSignalSpy coverage
for the card-added and download-settings signals, and assert explicitly that a
card row is a leaf with no child columns (the tester does not check that).

The contract checker immediately found four model bugs, fixed here:
- DeckListModel allowed children below non-zero columns.
- CardDatabaseModel reported every card as a child of every card row.
- CardDatabaseModel reported six columns for a valid (leaf) card index.
- CardDatabaseDisplayModel claimed more rows were fetchable while rowCount
  already exposed them all, so fetchMore() inserted duplicates.

Co-authored-by: Lukas Brübach <Bruebach.Lukas@bdosecurity.de>

libcockatrice_models/libcockatrice/models/database/card_database_display_model.cpp

@@ -33,8 +33,6 @@ CardDatabaseDisplayModel::CardDatabaseDisplayModel(QObject *parent)
         invalidate();
         emit modelDirty();
     });
-
-    loadedRowCount = 0;
 }
 
 void CardDatabaseDisplayModel::setSourceModel(QAbstractItemModel *model)
@@ -45,10 +43,7 @@ void CardDatabaseDisplayModel::setSourceModel(QAbstractItemModel *model)
 
     connect(model, &QAbstractItemModel::rowsRemoved, this, [this]() { dirty(); });
 
-    connect(model, &QAbstractItemModel::modelReset, this, [this]() {
-        loadedRowCount = 0;
-        dirty();
-    });
+    connect(model, &QAbstractItemModel::modelReset, this, [this]() { dirty(); });
 }
 
 QMap<wchar_t, wchar_t> CardDatabaseDisplayModel::characterTranslation = {{L'“', L'\"'},
@@ -56,32 +51,6 @@ QMap<wchar_t, wchar_t> CardDatabaseDisplayModel::characterTranslation = {{L'“'
                                                                          {L'‘', L'\''},
                                                                          {L'’', L'\''}};
 
-bool CardDatabaseDisplayModel::canFetchMore(const QModelIndex &index) const
-{
-    return loadedRowCount < sourceModel()->rowCount(index);
-}
-
-void CardDatabaseDisplayModel::fetchMore(const QModelIndex &index)
-{
-    int remainder = sourceModel()->rowCount(index) - loadedRowCount;
-    int itemsToFetch = qMin(100, remainder);
-
-    if (itemsToFetch == 0) {
-        return;
-    }
-
-    const auto startIndex = qMin(rowCount(QModelIndex()), loadedRowCount);
-    beginInsertRows(QModelIndex(), startIndex, startIndex + itemsToFetch - 1);
-
-    loadedRowCount += itemsToFetch;
-    endInsertRows();
-}
-
-int CardDatabaseDisplayModel::rowCount(const QModelIndex &parent) const
-{
-    return QSortFilterProxyModel::rowCount(parent);
-}
-
 bool CardDatabaseDisplayModel::lessThan(const QModelIndex &left, const QModelIndex &right) const
 {
     const QString leftString = sourceModel()->data(left, CardDatabaseModel::SortRole).toString();

libcockatrice_models/libcockatrice/models/database/card_database_display_model.h

@@ -42,7 +42,6 @@ private:
     QSet<QString> cardNameSet, cardTypes, cardColors;
     FilterTree *filterTree;
     FilterString *filterString;
-    int loadedRowCount;
     QTimer dirtyTimer;
     CardSearchLanguage searchLanguage;
     QString searchText;
@@ -85,9 +84,6 @@ public:
         dirtyTimer.start(20);
     }
     void clearFilterAll();
-    [[nodiscard]] int rowCount(const QModelIndex &parent = QModelIndex()) const override;
-    [[nodiscard]] bool canFetchMore(const QModelIndex &parent) const override;
-    void fetchMore(const QModelIndex &parent) override;
 signals:
     void modelDirty();
 

libcockatrice_models/libcockatrice/models/database/card_database_model.cpp

@@ -27,14 +27,18 @@ CardDatabaseModel::CardDatabaseModel(CardDatabase *_db, bool _showOnlyCardsFromE
 
 CardDatabaseModel::~CardDatabaseModel() = default;
 
-int CardDatabaseModel::rowCount(const QModelIndex & /*parent*/) const
+int CardDatabaseModel::rowCount(const QModelIndex &parent) const
 {
-    return cardList.size();
+    // A list model's card rows are leaves; returning the full card count for a
+    // valid parent makes every row claim all cards as children.
+    return parent.isValid() ? 0 : cardList.size();
 }
 
-int CardDatabaseModel::columnCount(const QModelIndex & /*parent*/) const
+int CardDatabaseModel::columnCount(const QModelIndex &parent) const
 {
-    return CARDDBMODEL_COLUMNS;
+    // Card rows are leaves, so a valid parent holds no columns. Reporting the
+    // row width for a card index would claim child cells that do not exist.
+    return parent.isValid() ? 0 : CARDDBMODEL_COLUMNS;
 }
 
 QVariant CardDatabaseModel::data(const QModelIndex &index, int role) const

libcockatrice_models/libcockatrice/models/deck_list/deck_list_model.cpp

@@ -134,6 +134,13 @@ void DeckListModel::rebuildTree()
 
 int DeckListModel::rowCount(const QModelIndex &parent) const
 {
+    // Only column 0 carries children. Column 1 and later indexes are siblings
+    // used by views for the remaining cells of a row, and a model that hangs
+    // children off them breaks QAbstractItemModelTester and proxy models.
+    if (parent.isValid() && parent.column() != 0) {
+        return 0;
+    }
+
     // debugIndexInfo("rowCount", parent);
     auto *node = getNode<InnerDecklistNode *>(parent);
     if (node) {
@@ -282,7 +289,7 @@ QVariant DeckListModel::headerData(const int section, const Qt::Orientation orie
 QModelIndex DeckListModel::index(int row, int column, const QModelIndex &parent) const
 {
     // debugIndexInfo("index", parent);
-    if (!hasIndex(row, column, parent)) {
+    if ((parent.isValid() && parent.column() != 0) || !hasIndex(row, column, parent)) {
         return {};
     }