I do:
if(parent.isValid() && parent.column() > 0) return 0;

Hope that helps.

int TreeModel::rowCount(const QModelIndex &parent) const
{
    if (parent.column() > 0)
        return 0; 

I.e. it simply reports no rows if asked for any column other than the left one. As result I assume there are no queries done for child indices outside the left column.

Probably it is right... but not obvious...

JohnGa gave a snippet of test case and my model fails at the last line:

MODELTESTER_VERIFY(childIndex != childIndex1);

I made it based on this example that hase following implementation of index() method:

QModelIndex TreeModel::index(int row, int column, const QModelIndex &parent) const
{
    if (!hasIndex(row, column, parent))
        return QModelIndex();

    TreeItem *parentItem;

    if (!parent.isValid())
        parentItem = rootItem;
    else
        parentItem = static_cast<TreeItem*>(parent.internalPointer());

    TreeItem *childItem = parentItem->child(row);
    if (childItem)
        return createIndex(row, column, childItem);
    return QModelIndex();
}

As I see the test do the following:
Creates first top index model->index(0, 0, QModelIndex())
Creates second top index model->index(0, 1, QModelIndex())
So three are 2 indices (0, 0, <void>) and (0, 1, <void) but both have the same value of internalPointer as childItem depends on row only.
As next step the test makes calls
model->index(0, 0, topIndex) and model->index(0, 0, topIndex1) with different parent indices, but - both of them have the same internal pointer. So the call parentItem->child(row) will provide the same value of the childItem.
And finally this return createIndex(row, column, childItem) will give two identical indices (0, 0, childItem) that will fail the test.

But I don't fully understand what is wrong with all this story.
My guess is that index() method should add childItem data only for column 0. But then parent() method of the example will fail. So I assume it should be changed to be more inteligente looking into internalPointer() of the first column. Is it right understanding or I miss something here?

int TreeModel::columnCount(const QModelIndex &parent) const
{
    return (!parent.isValid() || parent.column() == 0) ? rootItem->columnCount() : 0;
}

-> only the first column has sub-columns, not the second (which would look somehow strange)

It has no real-world impact in the Qt since the current implementation does first check for other things but is wrong when you want to catch all cases - the model tester is very picky here :). Will create a patch for it, thx.

Here are the steps to apply the modeltester to the editabletreemodel example:
1)after the editabletreemodel example has been setup in QtCreator, open the editabletreemodel.pro file. Add "testlib" to the this line "QT += widgets ".
2)Open mainwindow.cpp and add ```
"#include <QAbstractItemModelTester>"
3) Add the line shown below

//The line below is in the example
TreeModel *model = new TreeModel(headers, file.readAll());
//Add the line below
new QAbstractItemModelTester(model, QAbstractItemModelTester::FailureReportingMode::Fatal, this);

4)Run the example and you will see the above failures.

Thanks