test: verify the plugin works with Test Kitchen in CI

.github/workflows/integration.yml

@@ -0,0 +1,55 @@
+---
+name: "Test Kitchen"
+
+"on":
+  push:
+    branches: [main]
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
+jobs:
+  kitchen:
+    name: "kitchen verify on Ruby ${{ matrix.ruby }}"
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        # The ends of the supported range. The unit and feature suites already
+        # cover everything in between; this job is about the Test Kitchen
+        # integration, not Ruby compatibility.
+        ruby: ["3.2", "4.0"]
+    env:
+      # Outside the checkout on purpose. The runners require "bundler/setup",
+      # which walks up from the suite looking for a Gemfile -- so a Busser root
+      # inside the workspace finds this project's Gemfile and tries to
+      # materialize that bundle inside the isolated gem home, which fails. A
+      # real Busser root is /opt/busser, never inside the project.
+      BUSSER_ROOT: /tmp/busser-kitchen
+    steps:
+      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1  # v7.0.1
+
+      # Deliberately no bundler-cache, and nothing below runs under `bundle
+      # exec`. The verifier shells out to `gem list` to decide what to install,
+      # and bundler in the environment makes that report the bundle's gems
+      # rather than the Busser root's -- so it skips installing busser and the
+      # run dies on a path that was never created. Test Kitchen is not run from
+      # inside a project's bundle in real use either.
+      - uses: ruby/setup-ruby@95ef2b042f9d7a56d8268cba8559e2842e2ad01b  # v1.321.0
+        with:
+          ruby-version: ${{ matrix.ruby }}
+
+      - name: Install Test Kitchen
+        run: gem install test-kitchen --no-document --version "~> 4.1"
+
+      - name: Install this working tree into the Busser root
+        run: ./kitchen-preinstall.sh
+
+      - name: kitchen verify
+        run: kitchen verify

.gitignore

@@ -14,3 +14,4 @@ spec/reports
 test/tmp
 test/version_tmp
 tmp
+.kitchen/

kitchen-preinstall.sh

@@ -0,0 +1,55 @@
+#!/usr/bin/env bash
+# Installs this working tree into the Busser root the Test Kitchen verifier
+# will use, so `kitchen verify` exercises the code on this branch rather than
+# the last release from RubyGems.
+#
+# The verifier's install script skips its own install when `gem list` already
+# shows what it wants, so putting things in place first is all that is needed.
+# Two consequences to handle:
+#
+#   * It also has to install busser itself. That check is `grep "^busser"` with
+#     no anchor at the end, so a plugin named busser-* satisfies it and busser
+#     would otherwise never be installed at all.
+#   * Skipping `busser plugin install` also skips the plugin's postinstall,
+#     which is where a plugin installs the test framework it drives. So run the
+#     postinstall here, which is what the verifier would have done.
+set -euo pipefail
+
+BUSSER_ROOT="${BUSSER_ROOT:-/tmp/busser-kitchen}"
+gemspec="$(ls ./*.gemspec)"
+gem_name="$(basename "${gemspec}" .gemspec)"
+
+install_opts=(
+  --install-dir "${BUSSER_ROOT}/gems"
+  --bindir "${BUSSER_ROOT}/bin"
+  --no-document
+)
+
+mkdir -p "${BUSSER_ROOT}/gems"
+
+gem build "${gemspec}" --output "${BUSSER_ROOT}/${gem_name}.gem" >/dev/null
+
+if [ "${gem_name}" = "busser" ]; then
+  # No --local: a plugin's runtime dependencies are things its runner needs on
+  # the machine under test, and they have to be fetched into the Busser root
+  # like everything else.
+  gem install "${BUSSER_ROOT}/${gem_name}.gem" "${install_opts[@]}" >/dev/null
+else
+  gem install busser "${install_opts[@]}" >/dev/null
+  # Not --ignore-dependencies: a plugin's runtime dependencies are things its
+  # runner needs on the machine under test, and they have to be in the Busser
+  # root like everything else.
+  # No --local: a plugin's runtime dependencies are things its runner needs on
+  # the machine under test, and they have to be fetched into the Busser root
+  # like everything else.
+  gem install "${BUSSER_ROOT}/${gem_name}.gem" "${install_opts[@]}" >/dev/null
+
+  # The same environment the verifier exports, so the framework this plugin
+  # installs lands in the Busser root rather than the ambient gem home.
+  BUSSER_ROOT="${BUSSER_ROOT}" \
+    GEM_HOME="${BUSSER_ROOT}/gems" \
+    GEM_PATH="${BUSSER_ROOT}/gems" \
+    "${BUSSER_ROOT}/bin/busser" plugin install "${gem_name}" --force-postinstall
+fi
+
+echo "pre-installed ${gem_name} from the working tree into ${BUSSER_ROOT}"

kitchen.yml

@@ -0,0 +1,23 @@
+---
+# Runs the bash runner the way Test Kitchen actually runs it -- real verifier,
+# real busser, real suite transfer -- but against the machine running the tests
+# rather than a VM or container, so it works unchanged in CI.
+driver:
+  name: exec
+
+provisioner:
+  name: dummy
+
+verifier:
+  name: busser
+  # The verifier defaults to Chef's omnibus Ruby, which is not what is running
+  # here, and to sudo, which is not needed for a path under the workspace.
+  ruby_bindir: <%= RbConfig::CONFIG["bindir"] %>
+  sudo: false
+  root_path: <%= ENV.fetch("BUSSER_ROOT", "/tmp/busser-kitchen") %>
+
+platforms:
+  - name: local
+
+suites:
+  - name: default

test/integration/default/bash/helper.sh

@@ -0,0 +1,5 @@
+#!/usr/bin/env bash
+# Not named *_test.sh or *_spec.sh, so busser-bash must never run it. If the
+# glob ever widens, this fails the suite loudly.
+echo "helper.sh should not have been executed"
+exit 1

test/integration/default/bash/smoke_test.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+# Runs on the machine under test through busser-bash. Exit status is the verdict.
+set -euo pipefail
+
+test -n "$(command -v bash)"
+echo "busser-bash ran this script"