test: uts for areaChart, barChart, sparkAreaChart, Legend

[Wajahat5]

Description
Added new UTs for areaChart, barChart, sparkAreaChart, Legend components, and increased their coverage.

Added new files AreaChart.test.tsx, BarChart.test.tsx, SparkAreaChart.test.tsx and used existing file Legend.test.tsx to write UTs for areaChart, barChart, sparkAreaChart, Legend components.

Earlier the coverage for the said components looked like this:
All files | 49.66 | 22.91 | 35.94 | 50.76
AreaChart.tsx | 4 | 0 | 0 | 4.16 |
BarChart.tsx | 6 | 0 | 0 | 6.25 |
SparkAreaChart.tsx | 25 | 0 | 0 | 25 |
Legend.tsx | 35.29 | 23.88 | 28 | 35.36 |
Test Suites: 34 passed, 34 total
Tests: 45 passed, 45 total

After adding new tests, it looks like this:
File | % Stmts | % Branch | % Funcs | % Lines |
All files | 52.99 | 31.31 | 39.74 | 54.24
AreaChart.tsx | 28 | 43.08 | 20 | 29.16 |
BarChart.tsx | 28 | 42.2 | 16.66 | 29.16
SparkAreaChart.tsx | 100 | 72.72 | 100 | 100 |
Legend.tsx | 47.05 | 35.82 | 36 | 47.56 |
Test Suites: 37 passed, 37 total
Tests: 62 passed, 62 total

Related issue(s)
#1064

What kind of change does this PR introduce? (check at least one)

• Bug fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• New Feature (BREAKING CHANGE which adds functionality)
• Refactor
• Build-related changes
• Other, please describe:

• unit test cases for areaChart, barChart, sparkAreaChart, Legend components.

Does this PR introduce a breaking change? (check one)

• Yes
• No

How has this been tested?
By executing npm run tests -- --coverage --watchAll to get a report on the new ut coverage.
The changes does not effect other parts of the code as it only adds new tests.

The PR fulfils these requirements:

• It's submitted to the main branch
• When resolving a specific issue, it's referenced in the related issue section above
• My change requires a change to the documentation. (Managed by Tremor Team)
• I have added tests to cover my changes
• Check the "Allow edits from maintainers" option while creating your PR.
• Add refs #XXX or fixes #XXX to the related issue section if your PR refers to or fixes an issue.
• By contributing to Tremor, you confirm that you have read and agreed to Tremor's CONTRIBUTING.md guideline. You also agree that your contributions will be licensed under the Apache License 2.0 license.

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Name	Status	Preview	Comments	Updated (UTC)
tremor-storybook	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 26, 2024 7:21pm

[severinlandolt]

Nice! Will have a look at it in the next minor release 🚀