angular/components

bug(MatTree): MatTreeHarness with NestedTreeControl returns wrong structure

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#23,881 opened on Nov 3, 2021

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P3area: cdk/treehelp wanted

Description

Reproduction

Steps to reproduce:

  1. Create a MatTreeComponent with a NestedTreeControl and MatTreeNestedDatasource
  2. Test the component structure

https://stackblitz.com/edit/harness-issue-xgqlpl?file=src/app/tree-harness-example.spec.ts

Expected Behavior

The structure should have as many children (2 in the Stackblitz example) as visible Nodes.

{ children: [ { text: "Group 1"}, { text: "Group 2"} ] }

Actual Behavior

The structure has only one children without text.

{ children: [ { text: ""} ] }

Environment

  • Angular: 12.2.12
  • CDK/Material: 12.2.12
  • Browser(s): Test Environment
  • Operating System (e.g. Windows, macOS, Ubuntu): Windows

Contributor guide

Tech stack
typescriptangularhtml
Domain
frontendtesting
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Angular MaterialComponent test harnessesMatTree
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
30
Research direction
Examine the MatTreeHarness class and its getStructure method in the Angular Material source code. The reproduction demonstrates that for a NestedTreeControl, the structure only returns one child with empty text. Compare the implementation for NestedTreeControl versus FlatTreeControl. The fix likely involves correctly traversing the tree nodes using the control's expand and children accessors. Refer to the Stackblitz for exact setup.
bug(MatTree): MatTreeHarness with NestedTreeControl returns wrong structure · angular/components#23881 | Good First Issue