Refactoring and Code Quality in .NET: Analyzers, Sonar, Style, and Architecture Tests

This post covers practical code quality tools and refactoring habits for .NET teams: Roslyn analyzers, formatting rules, Sonar, architecture tests, and safe refactoring workflows. Code quality is not about making code look clever. It is about making change safer and cheaper.

Refactoring vs rewriting

Refactoring changes internal structure without changing external behavior. Rewriting replaces implementation more broadly.

Good refactoring:

• has tests or clear verification
• happens in small steps
• preserves behavior
• improves naming, boundaries, or duplication

Risky refactoring:

• changes too many behaviors at once
• mixes cleanup with feature work
• lacks tests around the affected paths
• moves code without improving clarity

Refactoring should reduce future cost, not create churn.

Roslyn analyzers

Roslyn analyzers inspect C# code at compile time.

Common analyzer categories:

• correctness
• style
• security
• performance
• API usage

Enable built-in analysis in .csproj:

<PropertyGroup>
  <AnalysisLevel>latest</AnalysisLevel>
  <TreatWarningsAsErrors>false</TreatWarningsAsErrors>
</PropertyGroup>

For mature projects, teams often turn selected warnings into errors.

EditorConfig

.editorconfig keeps formatting and style consistent.

Example:

[*.cs]
dotnet_style_qualification_for_field = false:suggestion
csharp_style_namespace_declarations = file_scoped:suggestion
dotnet_diagnostic.IDE0060.severity = warning

Consistent formatting reduces review noise. Developers should discuss design, behavior, and risk instead of whitespace.

Sonar and static analysis

SonarQube or SonarCloud can identify:

• bugs
• vulnerabilities
• code smells
• duplication
• test coverage gaps

Use static analysis as a signal, not as a substitute for engineering judgment. Not every finding has equal value, and suppressions should be intentional.

Architecture tests

Architecture tests verify dependency rules.

Example rule:

Domain must not depend on Infrastructure.

Conceptual test:

[Fact]
public void Domain_Should_Not_Depend_On_Infrastructure()
{
    var result = Types.InAssembly(typeof(Order).Assembly)
        .Should()
        .NotHaveDependencyOn("Store.Infrastructure")
        .GetResult();

    Assert.True(result.IsSuccessful);
}

Architecture tests are useful when boundaries are important and easy to accidentally violate.

Refactoring workflow

A safe workflow:

1. add or confirm tests around the behavior
2. make one structural change
3. run tests
4. repeat
5. keep commits focused

For large refactors, avoid mixing:

• renames
• behavior changes
• dependency upgrades
• formatting-only changes

Separate commits make review and rollback easier.

Code review signals

Look for:

• unclear names
• hidden side effects
• duplicated business rules
• missing error handling
• weak tests around changed behavior
• abstractions with no clear purpose

Do not chase theoretical purity while ignoring real bugs. Code quality should support delivery and reliability.

Common mistakes to avoid

Watch for these issues:

• treating analyzer output as a checklist without judgment
• doing broad cleanup in unrelated feature PRs
• creating abstractions before duplication proves they are needed
• ignoring architecture drift until it is expensive to fix
• refactoring without a way to verify behavior

Sustainable code quality comes from small habits repeated consistently: clear names, focused tests, useful analyzers, architecture boundaries, and disciplined refactoring.

Next Article: Building Production-Ready .NET Systems: A Practical Roadmap