assertTreeMatches

Asserts that the matched node and expected describe the same user interface - the same widgets, nested the same way, holding the same state - and returns this interaction for chaining.

Written for comparing a hand-built reference tree against a composed one - the structural counterpart of captureToImage. Where a pixel comparison says only that two screens differ, this names the widget that differs and the property it differs in.

setContent { Button("Save", onClick = {}) }

onNodeOfType<JButton>().assertTreeMatches(JButton("Save"))

expected is laid out at the matched node's size first, so a reference built for the comparison carries the bounds the composed tree was laid out at without the caller arranging one.

The walk is depth-first pre-order and the first difference it finds is the one reported. At each node it compares, in this order:

• the widget type;

• the bounds, so a tree laid out differently is a difference rather than something only a capture would show - the two roots on their size alone, since each stands in a tree of its own and a descendant's bounds are already relative to its parent;

• what every component carries: visible, enabled, opaque, the font, the colors, the insets, the border, the layout manager, the text, and the number of children, which is what makes the walk below compare like with like, then its name, cursor, sizes, tool tip, alignments, transfer handler and key strokes;

• what a stock layout manager holds, read from the container it lays out, along with the constraints it holds each child under;

• the state the widget's own kind holds, where both nodes are that kind: what it shows and what stands selected in it, the range it offers, the icons on it, and the columns, rows and tabs it is read through;

• what it answers assistive technology with.

A collaborator a widget delegates to is compared by what it holds where that is reachable: a model by the elements, rows or value it stands for, a document by its text, so two models built apart match on what they carry. One that holds nothing of its own - a renderer, a caret, a transfer handler - is compared by its class, the way a border is, and a library-installed one against a hand-built reference is a difference this reports. An icon is compared by its class and the space it takes, so a look and feel that builds its own icon per tree still matches, and two icons of one class and size are not told apart.

Listeners are not compared: one listener is never equal to another.

Parameters

Throws