test: add test getChartSpecWithContext with lineChart

[RubMaker]

[中文版模板 / Chinese template]

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• [ ] New feature
• [ ] Bug fix
• [ ] TypeScript definition update
• [ ] Bundle size optimization
• [ ] Performance optimization
• [ ] Enhancement feature
• [ ] Refactoring
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• [x] Test Case
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🔗 Related issue link

#215

🔗 Related PR link

🐞 Bugserver case id

💡 Background and solution

add unit test for getChartSpecWithContext() when chartType is linechart

📝 Changelog

Language	Changelog
🇺🇸 English	add unit test for getChartSpecWithContext() when chartType is linechart
🇨🇳 Chinese	为getChartSpecWithContext()添加单测(图标类型为折线图)

☑️ Self-Check before Merge

⚠️ Please check all items below before requesting a reviewing. ⚠️

• [x] Doc is updated/provided or not needed
• [x] Demo is updated/provided or not needed
• [x] TypeScript definition is updated/provided or not needed
• [x] Changelog is provided or not needed

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🚀 Summary

copilot:summary

🔍 Walkthrough

copilot:walkthrough

[666haiwen]

Besides this test case, you can also add a test case of line chart with color field.