Add integration test for the plugin's hello API endpoint

[hanzei]

Summary

This PR exercises mattermost/mattermost#35643 and add it as a default testing method to new plugins.

AI Summary

Adds a single integration test that runs the plugin on a real Mattermost server and confirms its API endpoint is reachable.

TestHelloEndpoint uses the testhelper package from mattermost/mattermost#35643 to spin up Postgres + Mattermost containers, deploy the bundle from dist/, and assert that GET /plugins/<plugin-id>/api/v1/hello returns 200 with Hello, world!. Unlike the existing httptest-based unit test, this exercises the full path: client → server auth → plugin ServeHTTP → handler.

testhelper is imported as a library rather than vendored into this repo, which is the difference from #241.

Makefile: make test / make test-ci now build the bundle first, since the test deploys it. Rather than adding a new variable, this reuses the existing MM_SERVICESETTINGS_ENABLEDEVELOPER single-arch path with DEFAULT_GOOS=linux DEFAULT_GOARCH=amd64 — building all five platform targets is wasted work when only one binary is ever loaded. mattermost-enterprise-edition is published for linux/amd64 only, so an arm64 host runs it emulated and the server inside still looks for plugin-linux-amd64; pinning the architecture rather than using the host default is what keeps this working on Apple Silicon.

That single-arch path named its output after DEFAULT_GOOS/DEFAULT_GOARCH without passing them to the compiler, so overriding them renamed the binary instead of cross-compiling it. Both are now passed through to go build.

Ticket Link

Related: mattermost/mattermost#35643
Supersedes: #241

Notes for reviewers

• This cannot merge until #35643 lands. server/public is pinned to that PR's head commit (v0.4.5-0.20260901113350-f076092fbcf6) because pluginapi/testhelper is not in a released version yet. It needs re-pinning to a real tag afterwards. The pin also pulls the go directive from 1.25 to 1.26.7.
• CI will now need Docker. The test job runs on ubuntu-latest, which has it, but each run will pull the ~1GB mattermost-enterprise-edition image.

Verification

From a clean dist/, make test passes in ~22s: ~6s bundle build, ~17s Go tests (nearly all of it the container work), 0.5s webapp. Confirmed the bundle contains exactly one binary, plugin-linux-amd64, and that file reports it as an ELF x86-64 executable.

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📝 Walkthrough

Walkthrough

The Go module and dependencies were updated. Developer-mode builds now set explicit platform values for Linux/amd64 test distributions. A new integration test validates an authenticated plugin endpoint response.

Changes

Developer build and integration test flow

Layer / File(s)	Summary
Go toolchain and dependency baseline go.mod	The module now targets Go 1.26.7. Mattermost server, Testify, and indirect dependencies were refreshed.
Developer build and endpoint validation Makefile, server/integration_test.go	Developer-mode builds set GOOS and GOARCH. The test and test-ci targets build the Linux/amd64 distribution. TestHelloEndpoint validates the authenticated plugin response.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: 🟡 Moderate · up to a4951

Parallel builds can overwrite or partially construct the plugin bundle used by the integration test, leading to unreliable test results or deployment of an incomplete artifact. This bounded merge-readiness issue should be fixed or explicitly accepted before merging.

Sequence Diagram(s)

sequenceDiagram
  participant TestHelloEndpoint
  participant testhelper.Setup
  participant MattermostServer
  participant PluginHTTPHandler
  TestHelloEndpoint->>testhelper.Setup: configure test server
  TestHelloEndpoint->>MattermostServer: send authenticated HTTP request
  MattermostServer->>PluginHTTPHandler: route plugin request
  PluginHTTPHandler-->>TestHelloEndpoint: return greeting response
  TestHelloEndpoint->>TestHelloEndpoint: assert status and response body

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🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files. (1 skipped: 1 …
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly identifies the main change: adding an integration test for the plugin's hello API endpoint.
Description check	✅ Passed	The description accurately explains the integration test, Makefile updates, dependency pinning, Docker requirement, and verification results.

Full details: Docstring Coverage

Explanation

Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 1 functions across 1 files. (1 skipped: 1 unsupported.)

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch add-plugin-testhelper-integration-test

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Actionable comments posted: 1

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Inline comments:
In `@Makefile`:
- Line 349: Update the recursive dist invocations in the affected Makefile
recipes to avoid concurrent builds with the top-level dist target, and ensure
bundle generation waits for server and webapp outputs before the integration
test deploys it. Use one ordered Make dependency graph or otherwise
serialize/separate outputs while preserving the existing build behavior.

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⛔ Files ignored due to path filters (1)

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📒 Files selected for processing (3)

• Makefile
• go.mod
• server/integration_test.go

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[fmartingr]

Great work. Are all those new indirect dependencies caused by the new public package dependencies?

[hanzei]

Yes, they are. The biggest is the docker runtime needed for testcontainers. Not much we can do about that.

[fmartingr]

Yes, they are. The biggest is the docker runtime needed for testcontainers. Not much we can do about that.

Yeah, I was thinking about dependency maintenance (security for example) and how that would affect public, but in the end we will need to maintain it in any form, even if it's in a separate package. plugins as well. 🤷‍♂️ Small side effect dependabot can help us with.

[hanzei]

None of these dependencies get compiled into the plugin bundle, right? This should not be a security concern.

[fmartingr]

None of these dependencies get compiled into the plugin bundle, right? This should not be a security concern.

Not on the final build, but we need to act on CVEs either way.