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Testing Chart.js Instance Type Assignment and Validation in Chart.js

This test suite validates instance assignment and type checking in Chart.js TypeScript implementations. It focuses on verifying proper type enforcement for chart data structures and context interfaces, ensuring type safety when working with chart instances and datasets.

Test Coverage Overview

The test coverage focuses on type checking and instance assignment validation for Chart.js components.

Validates scatter chart data structure typing
Tests dataset point radius callback function typing
Verifies chart context interface implementation
Checks type enforcement for dataset array assignments

Implementation Analysis

The testing approach utilizes TypeScript’s type system to verify correct typing of Chart.js instances and data structures.

Key implementation patterns include:

Interface definition for chart context
Type assertion testing using @ts-expect-error
Dataset type validation for scatter plot implementations

Technical Details

Testing infrastructure includes:

TypeScript compiler for static type checking
Chart.js type definitions
ts-expect-error annotations for negative test cases
Interface declarations for type validation

Best Practices Demonstrated

The test suite exemplifies strong typing practices in TypeScript testing.

Explicit interface definitions for type safety
Proper use of type assertions for error checking
Clear separation of chart instance and data structure typing
Comprehensive type validation for chart components

chartjs/chartJs

test/types/test_instance_assignment.ts

            
import { Chart } from '../../src/types.js';

const chart = new Chart('id', {
  type: 'scatter',
  data: {
    labels: [],
    datasets: [{
      data: [{ x: 0, y: 1 }],
      pointRadius: (ctx) => ctx.parsed.x,
    }]
  },
});

interface Context {
  chart: Chart;
}

const ctx: Context = {
  chart: chart
};

// @ts-expect-error Type '{ x: number; y: number; }[]' is not assignable to type 'number[]'.
const dataArray: number[] = chart.data.datasets[0].data;