test: cover null chart style validation

[ahfoysal]

Summary

• add a regression test for style: null chart input so it is rejected as invalid params before chart generation
• clean up the area chart tool description grammar
• keep the check local to callTool so the test does not call the remote chart service

Context

Issue #313 shows style: null reaching the renderer and failing with Cannot read properties of null. Current main already rejects that input at validation time; this PR locks that behavior down so it does not regress.

Verification

• npm install
• npm run build
• npm test -- --run __tests__/utils/callTool.spec.ts __tests__/charts/charts.spec.ts
• npm test -- --run
• npx biome check __tests__/utils/callTool.spec.ts src/charts/area.ts __tests__/charts/area.json
• git diff --check

Refs #313.

[gemini-code-assist]

Code Review

This pull request fixes a grammatical typo in the area chart description and adds a new unit test to verify that callTool rejects a null style parameter. The reviewer suggested simplifying the test case by removing optional parameters that are not relevant to the specific validation being tested.

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[ahfoysal]

The new test only checks for a generic -32602 error, so it does not actually prove that chart generation is skipped before any rendering work starts. If callTool() still invokes downstream generation and the renderer later throws the same error code, this test would pass anyway. I would either spy on the generation path or assert on the specific validation message/source so the regression stays pinned to the null-style guard.

[hustcc]

can help to fix the issue？

[ahfoysal]

Fixed in the latest commit. I updated the test to check the specific null style validation message and added a spy to make sure generateChartUrl is not called when validation fails.

Checked locally:

• npm test -- __tests__/utils/callTool.spec.ts
• npx biome check __tests__/utils/callTool.spec.ts
• npm run build

[ahfoysal]

Verified on branch with latest commit:

• npm run build
• npm test -- --run tests/utils/callTool.spec.ts tests/charts/charts.spec.ts
• npx biome check tests/utils/callTool.spec.ts src/charts/area.ts tests/charts/area.json

callTool now rejects style:null with the explicit validation message, and the generateChartUrl path is not reached for that case.

[hustcc]

this is not fix the issue, just add an test case. Process the style = null case, make it works, this is fix the issue.

[ahfoysal]

Updated. You were right — the previous change only tested the rejection path.

This now handles style: null by treating it the same as an omitted style, so chart generation continues normally. The test was updated to assert that generateChartUrl is called with style removed from the payload.

Checked locally:

• npm test -- --run __tests__/utils/callTool.spec.ts __tests__/charts/charts.spec.ts
• npx biome check src/utils/callTool.ts __tests__/utils/callTool.spec.ts
• npm run build