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gdi-rendering-tests

Write xUnit tests for System.Drawing Graphics, Bitmap, GraphicsPath, and Font rendering APIs.

1.2k|337|Updated Oct 13, 2022
Search Tags:#fluentassertions#winforms#Unit testing#XUnit#GDI+#bitmap verification#system.drawing
One-click install
npx skills add https://github.com/dotnet/dotnet --skill gdi-rendering-tests
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: gdi-rendering-tests
Source: https://github.com/dotnet/dotnet/tree/main/src/winforms/.github/skills/gdi-rendering-tests
Command: npx skills add https://github.com/dotnet/dotnet --skill gdi-rendering-tests

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

Writing tests for GDI+ rendering APIs requires verifying that drawing calls actually produce pixels, covering both integer and float overloads, and matching .NET version guards — this Skill codifies those conventions so tests are consistent and complete.

Core Features & Use Cases

  • Bitmap-Based Verification: Uses VerifyBitmapNotEmpty and VerifyBitmapEmpty helpers that lock bitmap bits and scan for non-zero pixels to confirm rendering occurred.
  • Overload and Version Coverage: Enforces separate integer/float overload tests, Draw/Fill pair coverage, and #if NET11_0_OR_GREATER guards matching the API under test.
  • GraphicsPath Point Validation: Verifies PathPoints arrays with FluentAssertions approximate comparison at 0.000001f precision.
  • Use Case: When adding a new DrawRoundedRectangle API to System.Drawing, generate the full test matrix — integer and float overloads, Draw and Fill variants, and GraphicsPath point assertions — following the established naming and disposal conventions.

Quick Start

Write unit tests for the new Graphics.DrawRoundedRectangle API following the GDI+ rendering test conventions.

Frequently Asked Questions about gdi-rendering-tests

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I test that a Graphics drawing method actually renders pixels?▼

Create a small Bitmap, get a Graphics from it, call the drawing API, then call VerifyBitmapNotEmpty. This helper locks the bitmap bits and scans the pixel buffer for any non-zero bytes, confirming something was rendered.

How do I test integer and float overloads of System.Drawing APIs?▼

Write separate tests for each overload, named with an Integer or Float suffix such as Graphics_DrawRoundedRectangle_Integer. Even when the integer overload delegates to the float version, test both to verify the Rectangle to RectangleF conversion.

How do I verify GraphicsPath points in unit tests?▼

Use FluentAssertions BeApproximatelyEquivalentTo on path.PathPoints with a precision of 0.000001f. Capture the actual PathPoints output from a test run first, then use those values as the expected data.

Should GDI+ rendering tests use WinFormsFact or Fact attributes?▼

Graphics tests do not require STA threads, so use standard xUnit [Fact] and [Theory] attributes rather than [WinFormsFact] or [WinFormsTheory]. The test project combines xUnit with FluentAssertions.

How do version guards work for new .NET drawing API tests?▼

Wrap tests in the same preprocessor directive as the API itself, currently #if NET11_0_OR_GREATER. This ensures tests compile and run only on target frameworks where the API exists.

What are the limitations of bitmap-based rendering verification?▼

VerifyBitmapNotEmpty only confirms that some pixels were drawn, not that the output matches an expected image. For font metrics, verify values fall within expected ranges since rendering varies across environments.

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