Tree validation

TreeValidator accumulates rules and applies them to a visual or logical tree. Validation returns the validator, whose IsValid, Failures, and Results properties expose the outcome.

using Avalonia.Controls;
using Avalonia.HeadlessTestingFramework;
using System.Linq;

var validator = TreeValidator.Create()
    .RequireName("submitButton")
    .RequireNames("username", "password", "email")
    .RequireType<Button>()
    .RequireExactCount<TextBox>(3)
    .RequireMinCount<Label>(2)
    .RequireMaxCount<ComboBox>(1)
    .RequirePattern("//StackPanel/Button")
    .RequireProperty("submitButton", Button.IsEnabledProperty, true)
    .RequireVisible("submitButton")
    .ForbidType<ProgressBar>()
    .ForbidPattern("//*[@Name='deprecatedControl']")
    .Custom("Buttons should be at least 80 pixels wide",
        root => root.FindAll<Button>().All(button => button.Width >= 80));

validator.ValidateVisualTree(window);
foreach (var failure in validator.Failures)
    Console.WriteLine($"{failure.RuleDescription}: {failure.Message}");

validator.AssertValid();

Use ValidateLogicalTree(root) for the logical hierarchy. AssertValid() throws TreeValidationException when a rule fails; GetSummary() provides a readable result for diagnostic output.

Additional rules include RequireNameOfType<T>, RequireEnabled, RequireChildOf, and RequireClass. Rules that query a tree need the relevant controls to have been attached and their templates created. Validate the logical tree when the requirement concerns application content rather than generated template visuals.