DiffCoverageTool

A .NET CLI tool that determines unit test code coverage specifically for newly added or modified code since a given commit. This helps ensure that new changes are adequately tested without being skewed by the overall project coverage percentage.

Prerequisites

• .NET 8.0 SDK (or whichever version you compiled the tool with)
• Git installed and accessible from the command line

How It Works

1. Runs git diff -U0 <base-ref> to find all added or modified lines in the target repository.
2. Runs dotnet test --collect:"XPlat Code Coverage" on the target repository to generate a Cobertura XML report.
3. Intersects the modified lines from Git with the coverage metrics from Cobertura to calculate exactly how much of your new code is covered by tests.

How to Run

Option 1: Using dotnet run (Recommended for testing)

You can run the tool directly from its source code directory. Open a terminal and navigate to the DiffCoverageTool folder, then use dotnet run:

# Syntax
dotnet run --project <path-to-DiffCoverageTool.csproj> "<path-to-target-repo>" <base-git-ref>

# Example: Run against your working directory, comparing against your last commit (HEAD~1)
dotnet run --project DiffCoverageTool.csproj "C:\path\to\your\project" HEAD~1

# Example: To check uncommitted changes only against HEAD
dotnet run --project DiffCoverageTool.csproj "C:\path\to\your\project" HEAD

Option 2: Build the executable and run it

If you want to compile it into a standalone executable:

# Build the tool
dotnet build -c Release

# Run the compiled executable directly
.\bin\Release\net8.0\DiffCoverageTool.exe "C:\path\to\your\project" HEAD~1

Troubleshooting

• "No modified files found": This means git diff -U0 <base-ref> didn't return any changes. Ensure you have made changes relative to the base reference.
• "Could not find coverage.cobertura.xml": The tool executes dotnet test --collect:"XPlat Code Coverage". If Coverlet doesn't generate this file, make sure your target project actually has tests and references coverlet.collector (which is included by default via dotnet new xunit).
• "No coverable new lines found": If your coverage file is generated but reports 0 lines, ensure that your application code and your test code are in separate projects (e.g., MyApp.Core and MyApp.Tests). By default, Coverlet excludes the assembly containing the tests from coverage reporting.