Testing Strategy

Relevant source files

The following files were used as context for generating this wiki page:

• Tests/SwiftDitherKitTests/DitherValueAndAccessibilityTests.swift
• Tests/SwiftDitherKitTests/DitherMotionTests.swift
• Tests/SwiftDitherKitTests/DitherRendererTests.swift
• Tests/SwiftDitherKitTests/DitherRasterTests.swift
• Tests/SwiftDitherKitTests/DitherSparkleTests.swift
• Tests/SwiftDitherKitTests/DitherMathTests.swift
• Tests/SwiftDitherKitTests/DitherRenderCacheTests.swift
• Tests/SwiftDitherKitConsumerTests/SwiftDitherKitConsumerTests.swift
• README.md

The testing strategy for SwiftDitherKit focuses on ensuring the accuracy of low-level raster rendering, mathematical geometric calculations, and the accessibility of complex visual data. The suite covers unit testing of internal kernels, integration testing of renderer outputs, and consumer-facing API verification.

Testing is primarily implemented using the XCTest framework, targeting critical components like the Bayer matrix dither kernels, Cartesian and Polar coordinate systems, and motion state transitions.

Sources: Tests/SwiftDitherKitTests/, README.md:120-125

Core Testing Pillars

The project divides its testing efforts into several functional areas to ensure stability across different rendering contexts and user settings.

1. Rendering and Raster Integrity

Tests verify that the DitherRenderer produces stable, non-empty rasters for all chart types (Area, Line, Bar, Pie, Radar). The strategy involves checking pixel counts and checksums to ensure determinism in the rendering pipeline.

• Checksum Verification: Ensures that identical inputs result in identical pixel data.
• Transparency Checks: Validates that empty data results in transparent rasters.
• Variant Testing: Confirms that different DitherVariant types (gradient, dotted, hatched, solid) produce distinct occupancy and checksums.

Sources: Tests/SwiftDitherKitTests/DitherRendererTests.swift:23-50, Tests/SwiftDitherKitTests/DitherRasterTests.swift:51-64

2. Mathematical and Geometric Accuracy

The DitherMathTests validate the underlying logic for coordinate transformations and data normalization.

• Band Calculation: Testing how series are overlaid, stacked, or normalized to percentages.
• Hit Testing: Verifying that touch/mouse coordinates correctly map to specific data points or series IDs.
• Interpolation: Ensuring resample logic correctly handles data point transitions.

Sources: Tests/SwiftDitherKitTests/DitherMathTests.swift:20-65, Tests/SwiftDitherKitTests/DitherMathTests.swift:105-130

3. Motion and Transition Logic

The test suite explicitly handles the state machine for chart animations, crossfades, and accessibility-related motion reductions.

The diagram shows the decision logic used by DitherRasterMotionDecision to select the appropriate animation style based on state changes.
Sources: Tests/SwiftDitherKitTests/DitherMotionTests.swift:27-57

Detailed Test Components

Functional Test Areas

Component	Test File	Focus
DitherKernel	DitherRasterTests.swift	Bayer matrix thresholds, backing size caps, and column painting.
Geometry	DitherMathTests.swift	Linear scales, polygon hit testing, and pie slice angles.
Accessibility	DitherValueAndAccessibilityTests.swift	Semantic descriptors, localized number formatting, and screen reader labels.
Sparkles	DitherSparkleTests.swift	Density, placement, and wink/flare animation cycles.
Cache	DitherRenderCacheTests.swift	LRU eviction policies and byte limit adherence.

Sources: Tests/SwiftDitherKitTests/DitherRasterTests.swift:15-20, Tests/SwiftDitherKitTests/DitherValueAndAccessibilityTests.swift:42-70, Tests/SwiftDitherKitTests/DitherRenderCacheTests.swift:7-20

Interaction and Accessibility Testing

Tests ensure that the DitherCartesianChartDescriptor and DitherPieChartDescriptor correctly translate visual marks into semantic data for assistive technologies.

• Locale Support: Verification that DitherValueFormat respects Locale for currency and precision.
• Selection Normalization: Testing that invalid or missing identifiers are dropped from the selection state.
• Content Direction: Ensuring Polar charts use .radialClockwise while Cartesian charts use standard directions.

Sources: Tests/SwiftDitherKitTests/DitherValueAndAccessibilityTests.swift:25-40, Tests/SwiftDitherKitTests/DitherValueAndAccessibilityTests.swift:72-90

Infrastructure and Automation

The testing strategy extends beyond unit tests to include linting and snapshot rendering as part of the development lifecycle.

Build and Lint Commands

The project utilizes the Swift toolchain for maintaining code quality:

• swift test: Executes the full suite of XCTest units.
• xcrun swift-format lint: Recursively checks style and formatting.
• dither-kit-snapshot: A custom command that uses SwiftUI's ImageRenderer on macOS to generate gallery previews.

Sources: README.md:120-125, Sources/DitherKitSnapshot/main.swift:10-25

Consumer API Verification

The SwiftDitherKitConsumerTests target validates that the public API remains accessible and functional when imported as a module. This ensures that initializers for DitherAreaChart, DitherLineChart, DitherBarChart, DitherSparkline, and others are correctly exposed to external callers.

Sources: Tests/SwiftDitherKitConsumerTests/SwiftDitherKitConsumerTests.swift:7-50

Conclusion

The SwiftDitherKit testing strategy provides high confidence in the rendering engine by combining strict mathematical validation with deterministic pixel-level checks. By covering everything from raw dither kernels to high-level accessibility descriptors, the strategy ensures the library remains reliable across diverse platform configurations and motion settings.