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Code Coverage and Static Analysis in C# |
Code coverage in C#
Code coverage is a metric that measures the percentage of your source code that is executed by your test suite. It is a valuable tool for assessing the quality and effectiveness of your tests, helping to identify untested areas of your code. High code coverage doesn't guarantee bug-free software, but it does indicate a more thorough and robust test suite.
Common metrics:
Line Coverage: The percentage of code lines executed.
Branch Coverage: The percentage of decision points (like if-else statements) that were evaluated for both true and false outcomes.
Function/Method Coverage: The percentage of methods that were called during tests.
Example with Coverlet and ReportGenerator:
Coverlet is a popular, open-source, and cross-platform code coverage tool for .NET. ReportGenerator can then convert the generated coverage data into a readable report.
Add packages: Add the coverlet.collector package to your test project and the ReportGenerator tool.
bash
dotnet add MyTestProject package coverlet.collector
dotnet tool install --global dotnet-reportgenerator-globaltool
Run tests with coverage: Execute your tests and collect the coverage data.
bash
dotnet test --collect:"XPlat Code Coverage"
Generate a report: Use ReportGenerator to create a human-readable report.
bash
reportgenerator "-reports:.\MyTestProject\coverage.cobertura.xml" "-targetdir:coveragereport"
This will create a coveragereport folder with an HTML file detailing your coverage results.
Tools for C#:
Coverlet: A cross-platform and open-source library that integrates with dotnet test.
Visual Studio Code Coverage: A built-in feature in Visual Studio Enterprise that provides graphical visualizations of code coverage.
JetBrains dotCover: A commercial tool that offers seamless integration with Visual Studio and Rider, continuous testing, and advanced analysis.
Static analysis tools in C#
Static analysis is the process of automatically checking source code for bugs, security vulnerabilities, code smells, and adherence to coding standards without executing the program. By "shifting left," developers can find and fix issues earlier in the development process, reducing costs and improving software quality.
Common checks:
Bugs: Detects potential errors like null reference dereferences or resource leaks.
Security Vulnerabilities: Identifies security risks such as SQL injection, hardcoded secrets, or insecure cryptography.
Code Smells: Highlights design flaws or anti-patterns that can hurt code maintainability.
Performance Issues: Suggests more efficient coding alternatives.
Code Style Enforcement: Ensures consistent formatting and conventions across a codebase.
Example with Roslyn Analyzers:
The .NET Compiler Platform ("Roslyn") is deeply integrated with C# development. It provides built-in analyzers that check for code quality and style and allows for external analyzers to be added. Starting with .NET 5.0, Roslyn analyzers are enabled by default for all projects.
Configure in .editorconfig: You can customize Roslyn analyzer behavior by adding a .editorconfig file to your project.
# .editorconfig file for C# projects
# Severity of the issue (error, warning, suggestion, or none)
dotnet_diagnostic.CA1822.severity = error
# Rule settings
# CA1822: Mark members as static where possible
csharp_style_qualify_field_access = true
Add external analyzers: You can extend the functionality by installing third-party analyzers via NuGet packages. For example, to add StyleCop.Analyzers:
bash
dotnet add package StyleCop.Analyzers
Run analysis: The analysis runs automatically as you type in Visual Studio and can be enforced during a build.
bash
dotnet build
Popular tools for C#:
Roslyn Analyzers: Microsoft's built-in framework that provides static analysis for code quality, style, and security.
SonarQube / SonarCloud: A popular platform that analyzes code for bugs, vulnerabilities, and code smells across multiple languages, including C#.
NDepend: A commercial static analyzer that uses metrics to evaluate maintainability, complexity, and other code characteristics.
Security Code Scan: An open-source Roslyn analyzer that specifically focuses on security vulnerabilities.
How they work together
Code coverage and static analysis complement each other perfectly to provide a holistic view of code quality.
Static analysis proactively identifies potential problems in your code's structure, style, and security before you run any tests.
Code coverage dynamically confirms the effectiveness of your tests by measuring how much of your code is exercised.
Example:
Static analysis could warn you about a complex method with a high cyclomatic complexity score.
Code coverage might then reveal that your tests only exercise one of the many possible paths through that complex method.
Using this combined information, you can focus on refactoring the problematic method to make it simpler and writing more targeted tests to cover the untested execution paths.
Code coverage tools measure how much of your code is exercised by automated tests. They help identify untested areas and improve test quality.
Static analysis tools inspect code without executing it. They help detect bugs, code smells, security flaws, and style violations early in the development cycle.
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