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test: golden-file test for the plugin's generated code #85
Description
Part of #44 (migration to the official Go MCP SDK). This is a safety net that has to exist before the migration, so every generator change shows up as a reviewable diff.
Problem
cmd/protoc-gen-go-mcp/mcp_test.go tests only kindToCastType and unexport. Nothing checks what the plugin actually generates.
Do
- Factor the plugin's generation out of
maininto a function a test can call (e.g.generate(*protogen.Plugin) error). Keepmain's behaviour identical. - Add a test that builds a
pluginpb.CodeGeneratorRequestforexamples/protos/example.protowithout protoc, usingprotodesc.ToFileDescriptorProto(examplev1.File_example_proto)plus its dependencies. The test runs the generator on it and compares the emittedexample_mcp.pb.gobyte for byte with the committedexamples/gen/example/v1/example_mcp.pb.go. - Add an
-updateflag (go test ./cmd/protoc-gen-go-mcp -run Golden -update) that rewrites the golden file. Document it in a comment at the top of the test.
Acceptance criteria
-
go test ./...passes, with the golden test comparing against the committed file. - Changing one emitted line in
mcp.gomakes the test fail with a readable diff. - No protoc or protoc plugins needed to run the tests.
- Generated output is unchanged by this PR.
Activity
erikist commentedon Oct 8, 2026
🤖 Factory: picked up by dispatcher; working on branch factory/85-test-golden-file-test-for-the.
erikist commentedon Oct 8, 2026
🤖 Factory: opened PR #96 with the golden-file test.
Note on approach: I deviated from the issue's suggested
protodesc.ToFileDescriptorProto(examplev1.File_example_proto)becauseprotoc-gen-gostripsSourceCodeInfo(and thus all comments) from the descriptor it embeds in the compiled example package, so that approach can't reproduce the comment-derived strings in the generated output. Instead the test parsesexample.protodirectly withgithub.com/bufbuild/protocompile(pure Go, no protoc binary/plugin involved), which retains comments. Details and test evidence are in the PR.test: golden-file test for the plugin's generated code (#85) (#96)