[md]Golden testing

The mcp-golden-munit module provides snapshot testing for MCP server specs. It captures your server's tools, resources, resource templates, prompts, and capabilities as a JSON golden file, then fails the test if the spec changes unexpectedly.

Adding the dependency

libraryDependencies += "net.andimiller.mcp" %%% "mcp-golden-munit" % "0.10.0" % Test

Scala.js note: Your project must configure scalaJSLinkerConfig ~= (_.withModuleKind(ModuleKind.CommonJSModule)) for the test to work on JS.

Writing a golden test

Extend McpGoldenSuite, override goldenFileName, and implement def server: IO[Server[IO]]:

import cats.effect.IO
import net.andimiller.mcp.core.server.{Server, ServerBuilder}
import net.andimiller.mcp.golden.McpGoldenSuite

class MyServerGoldenSuite extends McpGoldenSuite:
  override def goldenFileName = "my-server.json"

  def server: IO[Server[IO]] =
    ServerBuilder[IO]("my-server", "1.0.0").build

How it works

1. First run — the golden file doesn't exist yet, so the test creates src/test/resources/{goldenFileName} containing the server's full spec as JSON.
2. Subsequent runs — the test extracts the current spec and compares it against the golden file. Any difference fails the test with a diff.
3. Regenerating — delete the golden file and rerun the test to create a fresh snapshot.
4. CI — if the golden file is missing when the CI environment variable is set, the test fails immediately. Always run locally first to generate the file.