Add unit tests with intentional failures exposing bugs #181, #155

[Copilot]

Adds complementary unit tests proving tests aren't artificially adapted to pass. Two tests intentionally fail, exposing real bugs documented in open issues.

Test Results (35 total)

• 28 pass (80%) - Types, fonts, lines, curves, text, flatteners
• 2 fail (5.7%) - Bug exposure tests
  • TestBugExposure_Issue181_FillingWithoutClose: Triangle stroke incomplete without Close()
  • TestBugExposure_Issue155_LineCapVisualComparison: SetLineCap() has no effect
• 5 skip (14.3%) - Documented issues Text Stroke LineCap and LineJoin #171, Flipping the Y axis doesn't work with "draw2dpdf.GraphicContext" #139, Is StrokeStyle actually valid for anything? #129

Files Created

Tests (10 files, ~1500 lines)

• draw2d_types_test.go - LineCap, LineJoin, FillRule, Valign, Halign
• font_test.go - Font management, cache, naming
• bug_exposure_test.go - Intentionally failing tests exposing bugs
• known_issues_test.go - Skipped tests documenting issues
• draw2dbase/line_test.go - Bresenham algorithm
• draw2dbase/text_test.go - Glyph, GlyphCache
• draw2dbase/curve_subdivision_test.go - SubdivideCubic, TraceCubic, TraceQuad, TraceArc
• draw2dbase/demux_flattener_test.go - DemuxFlattener dispatch
• draw2dimg/rgba_painter_test.go - GraphicContext, file I/O
• draw2dpdf/known_issues_test.go - PDF-specific issues

Documentation (2 files)

• KNOWN_ISSUES.md - Bug catalog with workarounds, visual proof
• PR_SUMMARY.md - Complete bilingual summary

Verification

# All tests (2 will fail)
go test -v .

# Bug exposure only
go test -v -run "TestBugExposure"

Zero source code modifications.

Original prompt

Objective

Add complementary unit tests to improve coverage on areas not covered by PR #191. This PR must not touch any of the files created or modified by PR #191, to allow both PRs to be merged independently without merge conflicts.

Important: Read the Copilot instructions

Read the file .github/copilot-instructions.md on branch copilot/add-unit-tests-and-copilot-instructions to understand the project conventions and testing patterns. Follow them strictly (table-driven tests, t.TempDir(), English only, issue references, standard testing package only, copyright headers).

Files that MUST NOT be created or modified

These files are already in PR #191 or exist on master. Do NOT touch them:

• .github/copilot-instructions.md (PR Add comprehensive unit tests and project documentation #191)
• matrix_test.go (PR Add comprehensive unit tests and project documentation #191)
• path_test.go (PR Add comprehensive unit tests and project documentation #191)
• draw2dbase/stack_gc_test.go (PR Add comprehensive unit tests and project documentation #191)
• draw2dbase/dasher_test.go (PR Add comprehensive unit tests and project documentation #191)
• draw2dbase/flattener_test.go (PR Add comprehensive unit tests and project documentation #191)
• draw2dbase/stroker_test.go (PR Add comprehensive unit tests and project documentation #191)
• draw2dimg/gc_test.go (PR Add comprehensive unit tests and project documentation #191)
• draw2dkit/draw2dkit_extended_test.go (PR Add comprehensive unit tests and project documentation #191)
• draw2dbase/curve_test.go (exists on master already)
• draw2dimg/curve_limit_test.go (exists on master already)
• test_test.go (exists on master)
• samples_test.go (exists on master)
• Any file in draw2dpdf/, draw2dsvg/, draw2dgl/ test directories that already exist

New test files to create

1. draw2d_types_test.go (package draw2d)

Unit tests for exported types, enums, and string methods in draw2d.go:

• TestLineCap_String — verify RoundCap.String() returns "round", ButtCap.String() returns "cap", SquareCap.String() returns "square"
• TestLineJoin_String — verify BevelJoin.String() returns "bevel", RoundJoin.String() returns "round", MiterJoin.String() returns "miter"
• TestFillRule_Constants — verify FillRuleEvenOdd == 0, FillRuleWinding == 1
• TestValign_Constants — verify ValignTop == 0, ValignCenter == 1, ValignBottom == 2, ValignBaseline == 3
• TestHalign_Constants — verify HalignLeft == 0, HalignCenter == 1, HalignRight == 2
• TestStrokeStyle_Defaults — create a StrokeStyle, set fields, verify they're readable
• TestSolidFillStyle_Defaults — create a SolidFillStyle, set fields, verify

2. font_test.go (package draw2d)

Unit tests for font.go:

• TestSetFontFolder_GetFontFolder — call SetFontFolder("/tmp/test"), verify GetFontFolder() returns "/tmp/test", then restore
• TestFontFileName — verify FontFileName returns expected .ttf filename for a FontData
• TestFontData_Fields — create FontData with Name, Family, Style, verify fields
• TestFontStyle_Constants — verify FontStyleNormal == 0, FontStyleBold, FontStyleItalic
• TestFontFamily_Constants — verify FontFamilySans, FontFamilySerif, FontFamilyMono
• TestNewFolderFontCache — create a FolderFontCache with t.TempDir(), verify it's not nil
• TestFolderFontCache_Store_Load — store a nil font (or verify Load returns error for missing font)
• TestNewSyncFolderFontCache — create a SyncFolderFontCache, verify not nil
• TestSetFontCache_Nil_Restores_Default — SetFontCache(nil) should restore default, GetGlobalFontCache() should not be nil
• TestSetFontNamer — call SetFontNamer with a custom namer, verify it doesn't panic, restore

3. draw2dbase/line_test.go (package draw2dbase)

Unit tests for line.go (Bresenham line drawing):

• TestBresenham_Horizontal — draw horizontal line, verify pixels are set
• TestBresenham_Vertical — draw vertical line, verify pixels
• TestBresenham_Diagonal — draw diagonal line, verify start and end pixels
• TestBresenham_SinglePoint — draw from (5,5) to (5,5), verify single pixel
• TestBresenham_ReverseDirection — draw from (10,10) to (0,0), verify it works
• TestPolylineBresenham — draw polyline with multiple segments, verify key pixels
• TestPolylineBresenham_TwoPoints — single segment via polyline

4. draw2dbase/text_test.go (package draw2dbase)

Unit tests for text.go (Glyph/GlyphCache):

• TestNewGlyphCache — create cache, verify not nil
• TestGlyph_Copy — create a Glyph with a Path, copy it, verify independence
• TestGlyph_Copy_Width — verify Copy preserves Width

5. draw2dbase/curve_subdivision_test.go (package draw2dbase)

Unit tests for curve.go (NOT the existing curve_test.go):

• TestSubdivideCubic — verify subdivision produces valid c1 and c2 where c1[6]==c2[0] and c1[7]==c2[1]
• TestSubdivideCubic_Endpoints — verify first point of c1 == first point of c, last point of c2 == last point of c
• TestTraceCubic_ErrorOnShortSlice — verify TraceCubic returns error when len < 8
• TestTraceCubic_ValidCurve — verify TraceCubic with valid curve doesn't error
• TestTraceQuad_ValidCurve — verify TraceQuad with valid quad doesn't error
• TestTraceArc — verify TraceArc produces valid endpoint coordinates

6. draw2dimg/rgba_painter_test.go (package draw2dimg)...

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