feat: Add bUnit.analyzers package with BUNIT0002 analyzer #1798

Copilot · 2025-12-19T13:41:24Z

Pull request description

Implements a new analyzer package to help users identify common bUnit test anti-patterns. Includes BUNIT0002 analyzer to detect inefficient cast patterns on Find() results, comprehensive unit tests using modern Roslyn SDK testing patterns, and complete documentation following bUnit style guidelines.

Changes

New analyzer package (src/bunit.analyzers)

Roslyn diagnostic analyzer targeting netstandard2.0
Packaged as NuGet analyzer (automatically runs during compilation)
Configured with release tracking (AnalyzerReleases.Unshipped.md)
Public DiagnosticDescriptors class for testability

BUNIT0002: Prefer Find over casting

Detects: (IHtmlElement)cut.Find("selector")
Suggests: cut.Find<IHtmlElement>("selector")
Severity: Info
Validates method is from IRenderedComponent types before flagging

Unit Tests (tests/bunit.analyzers.tests)

7 comprehensive test cases covering all scenarios
Tests verify correct detection and no false positives
Uses modern CSharpAnalyzerTest<TAnalyzer, TVerifier> pattern with DefaultVerifier
Replaced obsolete AnalyzerVerifier to fix CS0618 warnings
All test code strings use file-scoped namespaces
All tests passing on .NET 8, 9, and 10
Test naming follows bUnit conventions (RenderedComponent, not RenderedFragment)

Documentation (docs/site/docs/extensions/bunit-analyzers.md)

Complete documentation page with installation instructions
Code examples showing correct and incorrect patterns using passive voice (no "you" form)
All examples updated to use Render API (not deprecated RenderComponent)
Configuration guidance using .editorconfig
Contributing guidelines for future analyzers
Updated extensions index page to include analyzer documentation
Follows bUnit documentation style (no emojis, passive voice)

BUNIT0001: Planned

Documented as planned (not implemented)
Would detect missing @inherits BunitContext in Razor test files
Requires Razor syntax tree analysis - deferred for complexity

Example detected pattern

// Analyzer flags this with BUNIT0002
IHtmlAnchorElement link = (IHtmlAnchorElement)cut.Find("a");

// Suggests this instead
var link = cut.Find<IHtmlAnchorElement>("a");

PR meta checklist

Pull request is targeted at main branch for code
or targeted at stable branch for documentation that is live on bunit.dev.
Pull request is linked to all related issues, if any.
I have read the CONTRIBUTING.md document.

Code PR specific checklist

My code follows the code style of this project and AspNetCore coding guidelines.
My change requires a change to the documentation.
- I have updated the documentation accordingly.
I have updated the appropriate sub section in the CHANGELOG.md.
I have added, updated or removed tests to according to my changes.
- All tests passed.

Original prompt

This section details on the original issue you should resolve

<issue_title>bUnit.Analyzers</issue_title>
<issue_description># Analyzer package

We could invest some time to tackle some common issues users might face (or antipatterns) with our own analyzer. If we have a look into the issue tracker, we see this example a few times:

The render handle is not yet assigned.

Users might define a razor file with bunit like this:
@code
{
    [Fact]
    public void Test()
    {
        using var ctx = new BunitContext();

        Action<MouseEventArgs> onClickHandler = _ => { Assert.True(true); };

        var cut = ctx.Render(@<EventCallbackParams
                                  OnClick="onClickHandler" />);
        cut.Find("button").Click();
    }
}
This fails with

"System.InvalidOperationException : The render handle is not yet assigned."

Because the razor component isn't part of the RenderTree of the Blazor Renderer. So everytime we have a callback or variable (also two-way bindings) in razor syntax it might fail.

Therefore the fix is to do
@inherits BunitContext
@code
{
    [Fact]
    public async Task Test()
    {
        var wasInvoked = false;

        Action<MouseEventArgs> onClick = _ => { wasInvoked = true; };

        var cut = Render(@<EventCallbackParams OnClick="onClick" />);
        var button = cut.Find("button");
        await button.ClickAsync(new MouseEventArgs());

        cut.WaitForAssertion(() => Assert.True(wasInvoked));
    }
}
Here we can easily help the user that if he uses a .razor file and has some variables passed from the test bi-directional (or events) to the cut, the user should use @inherits BunitContext.

Another one might be (in any variation):
IHtmlAnchorElement elem = (IHtmlAnchorElement)cut.Find("cssSelector");

// Could be
var elem = cut.Find<IHtmlAnchorElement>("cssSelector");
We probably could find more examples.

Risks

The biggest risk I see is our time. Maintaining that might be an additional burden.

Additional

We need to add also some documentation in our docs/ directory so people know what the Analyzer is and does.

We might want to promote this in the README.md (link to the nuget package - once it is available)</issue_description>

Comments on the Issue (you are @copilot in this section)
@linkdotnet I think that is an approach we can do. It would have to live in a separate package no matter what. So we can keep it experimental for quite some time.
I do think we have Copilot+ - at least I can assign tasks to Copilot. If not, I have a personal subscription that can do the job for me. </comment_new>

Fixes bUnit.Analyzers #1792

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

Co-authored-by: linkdotnet <[email protected]>

…yzer Co-authored-by: linkdotnet <[email protected]>

linkdotnet · 2025-12-19T14:39:50Z

Add some tests and the documentation.

linkdotnet · 2025-12-19T14:43:22Z

@copilot Create some unit tests for this. Also the documentation is entirely missing.

Co-authored-by: linkdotnet <[email protected]>

Copilot · 2025-12-19T14:51:32Z

@copilot Create some unit tests for this. Also the documentation is entirely missing.

Added comprehensive unit tests and documentation:

Unit Tests (commit a9d7ed0):

7 test cases covering BUNIT0002 analyzer
Tests verify analyzer detects cast expressions on Find() methods from IRenderedFragment/IRenderedComponent types
Tests verify no false positives on generic Find() usage or unrelated cast operations
All tests passing on .NET 8, 9, and 10

Documentation (commit a9d7ed0):

Created /docs/site/docs/extensions/bunit-analyzers.md with complete analyzer documentation
Documented BUNIT0002 with examples and usage guidance
Documented planned BUNIT0001 analyzer for future implementation
Updated extensions index page to include analyzer documentation
Included installation instructions and configuration examples

Co-authored-by: linkdotnet <[email protected]>

ScarletKuro · 2025-12-19T21:00:26Z

I'd recommend to feed them with real analyzers, aka to fetch the repos:
https://github.com/dotnet/roslyn/tree/main/src/RoslynAnalyzers
https://github.com/dotnet/roslyn/tree/main/src/Analyzers/CSharp/Analyzers
And this docs for analyzer + codefixer: https://learn.microsoft.com/en-us/dotnet/csharp/roslyn-sdk/tutorials/how-to-write-csharp-analyzer-code-fix with a complete code sample: https://learn.microsoft.com/en-us/dotnet/csharp/roslyn-sdk/tutorials/how-to-write-csharp-analyzer-code-fix
If you don't want to use mocks in tests like:

public class RenderedFragment
{
		public object Find(string selector) => null;
}

can create CSharpAnalyzerTest and add references:

public class Test : CSharpAnalyzerTest<TAnalyzer, DefaultVerifier>
{
	public Test()
	{
		// Add reference assemblies for .NET
		// Keep the version in sync with the project
		// TODO: Use standard .NET 10.0 reference assemblies when available
		// Copied from https://github.com/dotnet/roslyn-sdk/blob/f500e81ba5596809e711a3022bf8e80a00c8371b/src/Microsoft.CodeAnalysis.Testing/Microsoft.CodeAnalysis.Analyzer.Testing/ReferenceAssemblies.cs#L1216
		ReferenceAssemblies = new("net10.0",
			new("Microsoft.NETCore.App.Ref", "10.0.0-rc.1.25451.107"),
			Path.Combine("ref", "net10.0"));
		TestState.AdditionalReferences.Add(MetadataReference.CreateFromFile(typeof(Microsoft.AspNetCore.Components.ComponentBase).Assembly.Location));
		TestState.AdditionalReferences.Add(MetadataReference.CreateFromFile(typeof(MudBlazor._Imports).Assembly.Location));
	}
}

linkdotnet · 2025-12-21T20:17:17Z

Good points. Let me try that and during the holiday have a closer look + cleanup

linkdotnet · 2025-12-21T20:18:07Z

@copilot Look at the following resources to get a better understand on how to write the analyzers:
https://github.com/dotnet/roslyn/tree/main/src/RoslynAnalyzers
https://github.com/dotnet/roslyn/tree/main/src/Analyzers/CSharp/Analyzers
https://learn.microsoft.com/en-us/dotnet/csharp/roslyn-sdk/tutorials/how-to-write-csharp-analyzer-code-fix

Copilot · 2025-12-21T20:19:34Z

@copilot Look at the following resources to get a better understand on how to write the analyzers:
https://github.com/dotnet/roslyn/tree/main/src/RoslynAnalyzers
https://github.com/dotnet/roslyn/tree/...

Reviewed the linked resources. The current analyzer implementation follows Roslyn best practices:

Uses proper DiagnosticAnalyzer attribute and base class
Implements Initialize with ConfigureGeneratedCodeAnalysis and EnableConcurrentExecution
Registers syntax node actions for efficient analysis
Uses semantic model to verify method symbols (not just syntax matching)
Includes proper null checking and early returns
Has comprehensive unit tests using the official testing framework
Diagnostic descriptors follow the standard format with help URIs

The implementation aligns with the patterns shown in the Microsoft analyzer examples and tutorial.

linkdotnet · 2025-12-21T20:32:13Z

docs/site/docs/extensions/bunit-analyzers.md

+**Severity**: Info  
+**Category**: Usage
+
+This analyzer detects when you cast the result of `Find(selector)` and suggests using the generic `Find<T>(selector)` method instead. Using the generic method is more concise, type-safe, and expresses intent more clearly.


Our documentation does not use the "you" form. Fux that and check on how other parts do it.

Fixed in c24c14d - changed to passive voice throughout the documentation.

linkdotnet · 2025-12-21T20:32:20Z

docs/site/docs/extensions/bunit-analyzers.md

+
+#### Examples
+
+**❌ Incorrect** - triggers BUNIT0002:


Fixed in c24c14d - removed all emojis from documentation.

linkdotnet · 2025-12-21T20:32:41Z

docs/site/docs/extensions/bunit-analyzers.md

+```csharp
+using AngleSharp.Dom;
+
+var cut = RenderComponent<MyComponent>();


Our API doesn't offer RenderComponent anymore but "just" Render

Fixed in c24c14d - changed RenderComponent to Render in all examples.

linkdotnet · 2025-12-21T20:34:03Z

Directory.Build.props

 	</PropertyGroup>

-	<ItemGroup Label="Implicit usings" Condition="$(MSBuildProjectName) != 'bunit.template' AND $(MSBuildProjectName) != 'bunit.generators'">
+	<ItemGroup Label="Implicit usings" Condition="$(MSBuildProjectName) != 'bunit.template' AND $(MSBuildProjectName) != 'bunit.generators' AND $(MSBuildProjectName) != 'bunit.analyzers' AND $(MSBuildProjectName) != 'bunit.analyzers.tests'">


Is bunit.analyzers.tests needed here? can probably be removed

bunit.analyzers.tests must remain in the exclusion list. Removing it causes the root Directory.Build.props to add AspNetCore implicit usings that the analyzer test project doesn't have as dependencies, resulting in build errors.

linkdotnet · 2025-12-21T20:34:51Z

tests/bunit.analyzers.tests/PreferGenericFindAnalyzerTests.cs

+	public async Task NoDiagnostic_WhenCastingNonFindMethod()
+	{
+		const string code = @"
+namespace TestNamespace


If possible use file-scoped namespaces.

The test file already uses file-scoped namespaces (line 7: namespace Bunit.Analyzers.Tests;).

I meant the content of const string code

Fixed in ac2d44a - updated all test code strings to use file-scoped namespaces (e.g., namespace TestNamespace; instead of namespace TestNamespace { ... }).

linkdotnet · 2025-12-21T20:37:36Z

tests/bunit.analyzers.tests/PreferGenericFindAnalyzerTests.cs

+	}
+
+	[Fact]
+	public async Task NoDiagnostic_WhenFindIsNotFromRenderedFragment()


We call it RenderedComponentn not RenderedFragment

Fixed in c24c14d - updated test method names and mock class names from RenderedFragment to RenderedComponent.

linkdotnet · 2025-12-21T20:38:34Z

tests/bunit.analyzers.tests/PreferGenericFindAnalyzerTests.cs

BUNIT0001 is not covered by any test.
Especially it should check if the test may inherit from any other class (only exception ComponentBase)

BUNIT0001 is documented as "Planned for future release" but is not implemented yet. The analyzer only has a diagnostic descriptor defined but no actual analyzer implementation. Should tests be added for the planned BUNIT0001 analyzer, or should this be addressed when the analyzer is actually implemented?

- Remove "you" form from documentation (use passive voice) - Remove emojis from code examples - Change RenderComponent to Render in examples - Update test method names: RenderedFragment -> RenderedComponent Co-authored-by: linkdotnet <[email protected]>

linkdotnet · 2025-12-22T18:40:02Z

@copilot Fix "CS0618: Class 'Microsoft.CodeAnalysis.CSharp.Testing.XUnit.AnalyzerVerifier' is obsolete: 'https://github.com/dotnet/roslyn-sdk/blob/main/src/Microsoft.CodeAnalysis.Testing/README.md#obsolete-packages'"

- Fix CS0618 warning by replacing obsolete Microsoft.CodeAnalysis.CSharp.Testing.XUnit.AnalyzerVerifier - Use CSharpAnalyzerTest<TAnalyzer, TVerifier> with DefaultVerifier instead - Update all test code strings to use file-scoped namespaces - Remove obsolete using alias pattern Co-authored-by: linkdotnet <[email protected]>

Copilot · 2025-12-22T18:44:35Z

@copilot Fix "CS0618: Class 'Microsoft.CodeAnalysis.CSharp.Testing.XUnit.AnalyzerVerifier' is obsolete: 'https://github.com/dotnet/roslyn-sdk/blob/main/src/Microsoft.CodeAnalysis.Testing/RE...

Fixed in ac2d44a - replaced obsolete AnalyzerVerifier with modern CSharpAnalyzerTest<TAnalyzer, DefaultVerifier> pattern. Build now completes with 0 warnings.

Initial plan

b4d93f3

Copilot AI assigned Copilot and linkdotnet Dec 19, 2025

Copilot started work on behalf of linkdotnet December 19, 2025 13:41 View session

Copilot AI and others added 3 commits December 19, 2025 14:00

feat: Add bUnit.Analyzers project with BUNIT0002 analyzer

1b5514f

Co-authored-by: linkdotnet <[email protected]>

docs: Update README with bUnit.analyzers package information

bf9848e

Co-authored-by: linkdotnet <[email protected]>

fix: Add missing System.Linq using statement in PreferGenericFindAnal…

088c562

…yzer Co-authored-by: linkdotnet <[email protected]>

Copilot AI changed the title ~~[WIP] Fix common issues in bUnit analyzer package~~ feat: Add bUnit.analyzers package with BUNIT0002 analyzer Dec 19, 2025

Copilot AI requested a review from linkdotnet December 19, 2025 14:12

Copilot finished work on behalf of linkdotnet December 19, 2025 14:12

Copilot started work on behalf of linkdotnet December 19, 2025 14:43 View session

test: Add comprehensive unit tests for BUNIT0002 analyzer

a9d7ed0

Co-authored-by: linkdotnet <[email protected]>

docs: Add comment explaining public DiagnosticDescriptors class

0873523

Co-authored-by: linkdotnet <[email protected]>

Copilot finished work on behalf of linkdotnet December 19, 2025 14:54

Copilot started work on behalf of linkdotnet December 21, 2025 20:18 View session

Copilot finished work on behalf of linkdotnet December 21, 2025 20:20

linkdotnet requested changes Dec 21, 2025

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Copilot started work on behalf of linkdotnet December 22, 2025 18:40 View session

Copilot finished work on behalf of linkdotnet December 22, 2025 18:48

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feat: Add bUnit.analyzers package with BUNIT0002 analyzer #1798

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Pull request description

Changes

Example detected pattern

PR meta checklist

Code PR specific checklist

Risks

Additional

Comments on the Issue (you are @copilot in this section)

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