Add test coverage for generate function

[Copilot]

The generate function lacked test coverage for validation logic, error handling, and tile generation workflows.

Changes

• main_test.ts: 9 tests covering successful generation (default/degrees/custom output), input validation (missing/non-existent files), angle bounds checking, and dimension validation
• main.ts: Exported generate function for testing
• deno.json: Added test task
• README.md: Added testing section with deno task test usage

Test Scenarios

// Successful generation
await generate({ input: "image.png", angleOption: 0 });
await generate({ input: "image.png", degrees: 45 });

// Error handling
await generate({ input: "/nonexistent.png" }); // throws
await generate({ angleOption: 999 }); // throws
await generate({ angleOption: 7, maxValidSize: 100 }); // dimension validation

Tests use temporary files in /tmp with cleanup in finally blocks.

Warning

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I tried to connect to the following addresses, but was blocked by firewall rules:

• dl.deno.land
  • Triggering command: /usr/bin/curl curl -s REDACTED (dns block)
  • Triggering command: /usr/bin/curl curl --fail --location --progress-bar --output /home/REDACTED/.deno/bin/deno.zip REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

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This section details on the original issue you should resolve

<issue_title>Add tests for generate main function</issue_title>
<issue_description></issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Add tests for generate main function #27

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