test(source/cloud-sql-mysql): create MCP integration tests

[dishaprakash]

Description

This PR migrates the Cloud SQL MySQL integration tests to use the /mcp endpoint on the MCP Toolbox Server.

Key Changes

• tests/mcp_tool.go:

  • Added modular builder functions (Base, ExecuteSQL, TemplateParams) to dynamically generate expected MCP manifests.
  • Added concatenation of individual MCP text blocks into a fully formatted JSON array whenever the test expects one, preserving compatibility with previous test assertions.

• cloud_sql_mysql_mcp_test.go: Migrated legacy /api tests to /mcp. Added negative parameter validation.

• cloud_sql_mysql_create_instance_mcp_test.go: Migrated create-instance tests to validate MCP JSON-RPC handling.

• tests/source.go: Added a WithMCP() option to RunSourceConnectionTest to verify database connections natively during MCP server init.

• tests/tool.go: Introduced ToolExecOption and the WithMCPExec() functional option to the prebuilt tool test harnesses. This enables the reuse of complex test cases, data structs, and assertions across both legacy /api and new /mcp endpoints by toggling the request routing and response parsing logic.

PR Checklist

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🛠️ Fixes #<issue_number_goes_here>

[gemini-code-assist]

Code Review

This pull request introduces comprehensive integration tests for the Model Context Protocol (MCP) across various data sources, including AlloyDB, Cloud SQL MySQL, and HTTP. It also adds modular helper functions in tests/mcp_tool.go to facilitate standardized MCP tool testing. Several issues were identified in the review: a critical flaw in the Cloud SQL MySQL instance creation test where mocking http.DefaultClient fails to affect the separate toolbox process, and multiple violations of the repository style guide regarding tool naming conventions (snake_case and product name exclusion). Additionally, the use of time.Sleep in MySQL tests was flagged as a potential source of flakiness, and some error assertions were noted as being too weak.