Interaction with other components

[Robelind]

Consider the following two components:
Component A:

<ComponentB @ref="@_componentB"/>   
<button @onclick="() => _componentB.Show()">Show</button>
@code {
    private ComponentB _componentB;
}

Component B:

@(_show ? "Hello world" : null)
@code {
    private bool _show;
    public void Show()
    {
        _show = !_show;
        StateHasChanged();
    }
}

When unit testing clicking the button in component A, I ideally only want to assert that ComponentB.Show() was called.
Any thoughts on the possibility of achieving this?

[egil]

Something like this should work:

var cut = RenderComponent<ComponentA>();

cut.Find("button").Click();

Assert.IsTrue(cut.Markup.StartsWith("Hello world"));

[Robelind]

Yes, of course, but now I'm testing both component A and component B.
What component B renders should be tested in isolated tests for component B.

[egil]

var cut = RenderComponent<ComponentB>();

cut.InvokeAsync(() => cut.Instance.Show());

Assert.Equals("Hello world", cut.Markup);

You can learn more about this on https://bunit.egilhansen.com/docs/verification/index.html and related pages.