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<title>Disposing components and their children | bUnit </title>
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<meta name="title" content="Disposing components and their children | bUnit ">
<meta name="description" content="bUnit is a unit testing library for Blazor Components. You can easily define components under test in C# or Razor syntax and verify outcome using semantic HTML diffing/comparison logic. You can interact with and inspect components, trigger event handlers, provide cascading values, inject services, mock IJsRuntime, and perform snapshot testing.">
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<article data-uid="dispose-components">
<h1 id="disposing-components">Disposing components</h1>
<p>To dispose all components rendered with a <code>BunitContext</code>, use the <a class="xref" href="../../api/Bunit.BunitContext.html#Bunit_BunitContext_DisposeComponentsAsync"><code>DisposeComponents</code></a> method. Calling this method will dispose all rendered components, calling any <code>IDisposable.Dispose</code> or/and <code>IAsyncDisposable.DisposeAsync</code> methods they might have, and remove the components from the render tree, starting with the root components and then walking down the render tree to all the child components.</p>
<p>Disposing rendered components enables testing of logic in <code>Dispose</code> methods, e.g., event handlers, that should be detached to avoid memory leaks.</p>
<p>The following example of this:</p>
<pre><code class="lang-csharp" name="DisposeComponentsTest.cs">var calledTimes = 0;
var cut = Render<DisposableComponent>(parameters => parameters
.Add(p => p.LocationChangedCallback, url => calledTimes++)
);
await DisposeComponentsAsync();
Services.GetRequiredService<NavigationManager>().NavigateTo("newurl");
Assert.Equal(0, calledTimes);
</code></pre>
<div class="WARNING">
<h5>Warning</h5>
<p>For <code>IAsyncDisposable</code> (since .net5) relying on <a class="xref" href="../../api/Bunit.RenderedComponentWaitForHelperExtensions.html#Bunit_RenderedComponentWaitForHelperExtensions_WaitForState__1_Bunit_IRenderedComponent___0__System_Func_System_Boolean__System_Nullable_System_TimeSpan__"><code>WaitForState()</code></a> or <a class="xref" href="../../api/Bunit.RenderedComponentWaitForHelperExtensions.html#Bunit_RenderedComponentWaitForHelperExtensions_WaitForAssertion__1_Bunit_IRenderedComponent___0__System_Action_System_Nullable_System_TimeSpan__"><code>WaitForAssertion()</code></a> will not work as a disposed component will not trigger a new render cycle.</p>
</div>
<h2 id="disposing-components-asynchronously">Disposing components asynchronously</h2>
<p>If a component implements <code>IAsyncDisposable</code>, <code>DisposeComponentsAsync</code> can be awaited to wait for all asynchronous <code>DisposeAsync</code> methods. Sometimes interacting with JavaScript in Blazor WebAssembly requires disposing or resetting state in <code>DisposeAsync</code>.</p>
<pre><code class="lang-csharp" name="DisposeComponentsTest.cs">JSInterop.SetupVoid("dispose").SetVoidResult();
Render<AsyncDisposableComponent>();
await DisposeComponentsAsync();
JSInterop.VerifyInvoke("dispose");
</code></pre>
<p>To omit this behavior, discard the returned task</p>
<pre><code class="lang-csharp">_ = DisposeComponentsAsync();
</code></pre>
<h2 id="checking-for-exceptions">Checking for exceptions</h2>
<p>Both <code>Dispose</code> and <code>DisposeAsync</code> can throw exceptions, which can be asserted during tests. When a component under test throws an exception in either <code>Dispose</code> or <code>DisposeAsync</code>, the exception is caught by the renderer and made available via the <code>Renderer.UnhandledException</code> task. The <code>DisposeComponentsAsync</code> method itself will not throw the exception.</p>
<p>This allows for consistent testing of exceptions during disposal, regardless of whether the disposal is synchronous or asynchronous.</p>
<p>The following examples demonstrate how to assert that an exception was thrown during disposal:</p>
<p><strong>Asserting exception in <code>Dispose</code>:</strong></p>
<pre><code class="lang-csharp" name="DisposeComponentsTest.cs">
[Fact]
public async Task ShouldCatchExceptionInDispose()
{
Render<ExceptionInDisposeComponent>();
await DisposeComponentsAsync();
var exception = await Renderer.UnhandledException;
Assert.IsType<NotSupportedException>(exception);
</code></pre>
<p><strong>Asserting exception in <code>DisposeAsync</code>:</strong></p>
<pre><code class="lang-csharp" name="DisposeComponentsTest.cs">
[Fact]
public async Task ShouldCatchExceptionInDisposeAsync()
{
Render<ExceptionInDisposeAsyncComponent>();
await DisposeComponentsAsync();
var exception = await Renderer.UnhandledException;
Assert.IsType<NotSupportedException>(exception);
</code></pre>
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