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Catalog/docs/image-generation-tests-plan.md
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Image generation test plan — ImageSharp-only (multiplatform)

Goal

Create an automated, cross-platform test project that validates ImageCreatorImageSharp behavior by generating synthetic input images and pixel-inspecting outputs produced by the library.

Decisions

  • Test only ImageCreatorImageSharp (multiplatform).
  • Test project targets net10.0 (not Windows-only) and uses SixLabors.ImageSharp for both generation and verification; avoid System.Drawing.Common in tests.
  • Inputs are programmatically generated images (no checked-in large binaries).
  • Verification uses pixel inspection (sample regions, color averages, non-background pixel counts).

Project

  • Name: MaddoShared.ImageSharpTests (folder: MaddoShared.ImageSharpTests/)
  • TargetFramework: net10.0 (no Windows-only flags)
  • Package references:
    • MSTest.TestFramework / MSTest.TestAdapter / Microsoft.NET.Test.Sdk
    • FluentAssertions
    • Moq (if needed for loggers)
    • SixLabors.ImageSharp and SixLabors.ImageSharp.Drawing (for image creation and pixel inspection)
    • Microsoft.Extensions.Logging.Abstractions (lightweight logging)
  • ProjectReference: ../MaddoShared/MaddoShared.csproj

Helpers (tests)

  • TempWorkspace — creates temporary Source and Dest folders, cleans up on dispose.
  • TestImageFactory — creates synthetic JPEG/PNG inputs and in-memory logo PNG bytes. Also can write EXIF orientation values.
  • PixelInspector — loads output using ImageSharp and exposes:
    • CountNonBackgroundPixels(path, Rectangle region, Rgba32 background, int tolerance)
    • SampleAverageColor(path, Rectangle region)
    • Region helpers: top/bottom/left/right/center/quadrant rectangles for given image sizes
  • CreatorFactory — builds PicSettings defaults and ImageCreatorImageSharp instances.

Test cases (high-level)

  1. Image resizing: verify big and small output dimensions respect settings.
  2. Text positioning: for Posizione = ALTO/CENTRO/BASSO and Allineamento = SINISTRA/CENTRO/DESTRA assert text pixels appear in expected regions.
  3. Text content: baseline (empty) vs non-empty comparisons to ensure text changes output; EXIF-vertical photo selects TestoFirmaV.
  4. Logo positioning: use a solid-color logo (e.g., pure red PNG) and verify red pixels appear in the expected quadrant for combinations of LogoPosizioneH × LogoPosizioneV and with margins (absolute and percentage).
  5. Logo features: opacity (logo color blending) and color-key transparency.
  6. EXIF orientation: ensure rotation is applied and output contains no EXIF orientation tag.

Verification approach

  • For text: compare non-background pixel count in the target band vs opposite band (thresholded) to avoid brittle exact glyph placement checks.
  • For logo: sample the quadrant where the logo should be; count logo-colored pixels and assert above threshold.
  • For opacity: sample average color in logo region and assert it is blended when opacity <100%.

Scope boundaries

  • In scope: ImageCreatorImageSharp behavior: resize, EXIF rotation, text presence/position, logo position/opactiy, thumbnails.
  • Out of scope: OCR verification of exact text glyphs, font-subpixel metrics, performance testing.

Implementation notes

  • Keep tests deterministic by creating solid-color inputs and simple logos.
  • Use modest image sizes (e.g., 800×600) so tests run fast.
  • Carefully choose thresholds for pixel-count assertions to be robust across fonts and rendering differences.

Run & validate

  • Build: dotnet build MaddoShared.ImageSharpTests
  • Test: dotnet test MaddoShared.ImageSharpTests

Files to add

  • MaddoShared.ImageSharpTests/MaddoShared.ImageSharpTests.csproj
  • MaddoShared.ImageSharpTests/Helpers/TempWorkspace.cs
  • MaddoShared.ImageSharpTests/Helpers/TestImageFactory.cs
  • MaddoShared.ImageSharpTests/Helpers/PixelInspector.cs
  • MaddoShared.ImageSharpTests/Helpers/CreatorFactory.cs
  • MaddoShared.ImageSharpTests/Tests/ImageResizingTests.cs
  • MaddoShared.ImageSharpTests/Tests/TextPositioningTests.cs
  • MaddoShared.ImageSharpTests/Tests/LogoPositioningTests.cs
  • MaddoShared.ImageSharpTests/Tests/ExifOrientationTests.cs
  • docs/image-generation-tests-plan.md (this file)

Next steps

  1. Create the MaddoShared.ImageSharpTests project and add the helper files.
  2. Implement the first set of tests (resizing + a simple text presence test) to validate the testing harness.
  3. Iterate thresholds and add remaining tests.