test(spread): add support for spread tests

.gitmodules

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+[submodule "tools/external"]
+	path = tools/external
+	url = https://github.com/snapcore/snapd-testing-tools.git
+	branch = main

spread.yaml

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+project: snapcraft-rocks
+
+# note: the `path` is inside /root because the docker snap has issues
+# mounting directories that are outside the user's home
+path: /root/snapcraft-rocks
+environment:
+  PROJECT_PATH: /root/snapcraft-rocks
+  SNAPD_TESTING_TOOLS: $PROJECT_PATH/tools/external/tools
+  PATH: /snap/bin:$PATH:$SNAPD_TESTING_TOOLS:$PROJECT_PATH/tools/spread
+  # This variable is used to set the base in multi-base projects
+  SNAPCRAFT_BASE: core22
+
+include:
+    - tests/
+    - tools/
+
+backends:
+  google:
+    key: '$(HOST: echo "$SPREAD_GOOGLE_KEY")'
+    location: snapd-spread/us-east1-b
+    halt-timeout: 2h
+    systems:
+      - ubuntu-20.04-64:
+          workers: 2
+          storage: 40G
+      - ubuntu-22.04-64:
+          workers: 2
+          storage: 40G
+      - fedora-37-64:
+          workers: 2
+          storage: 40G
+
+prepare: |
+  # if the 'tools' directory inside the submodule does not exist, then assume the submodule is empty
+  if [[ ! -d "$SNAPD_TESTING_TOOLS" ]]; then
+    echo "Cannot run spread because submodule 'snapd-testing-tools' is empty. Fetch with 'git submodule update --init' and rerun spread."
+    exit 1
+  fi
+
+  if os.query is-ubuntu; then
+    tempfile="$(mktemp)"
+    if ! apt-get update > "$tempfile" 2>&1; then
+        cat "$tempfile"
+        exit 1
+    fi
+  fi
+
+  tests.pkgs install snapd
+
+  snap wait system seed.loaded
+
+  # The /snap directory does not exist in some environments
+  [ ! -d /snap ] && ln -s /var/lib/snapd/snap /snap
+
+  # Hold snap refreshes for 24h.
+  snap set system refresh.hold="$(date --date=tomorrow +%Y-%m-%dT%H:%M:%S%:z)"
+  if ! snap watch --last=auto-refresh?; then
+      journalctl -xe
+  fi
+  if ! snap watch --last=install?; then
+      journalctl -xe
+  fi
+
+  if [ "$SPREAD_SYSTEM" = "fedora-37-64" ]; then
+    # Latest docker snap needs a more recent version of snapd than Fedora ships
+    # https://github.com/canonical/rockcraft/pull/277
+    snap install docker --channel=core18/stable
+  else
+    snap install docker
+  fi  
+
+  # make sure docker is working
+  retry -n 10 --wait 2 sh -c 'docker run --rm hello-world'
+  
+  # install rockcraft just to use its bundled skopeo
+  snap install --classic --stable rockcraft
+
+  load_snapcraft_rock
+
+
+restore-each: |
+  # Cleanup after each task.
+  rm -f *.snap
+
+
+suites:
+  tests/spread/general/:
+    summary: general tests that should work on all bases and Snapcraft versions

tests/spread/general/hello/snap/snapcraft.yaml

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+name: hello-world
+version: "1.0"
+summary: test
+description: hello-world
+grade: devel
+confinement: strict
+base: SNAPCRAFT_BASE
+
+parts:
+  hello-world:
+    plugin: nil
+    stage-packages: ["hello"]
+
+apps:
+  hello-world:
+    command: usr/bin/hello

tests/spread/general/hello/task.yaml

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+summary: build & run a basic "hello world" snap
+
+execute: |
+  # pack the snap
+  run_snapcraft pack
+
+  # install & run it
+  snap install --dangerous hello-world_1.0_amd64.snap
+  hello-world -g "hello-from-snap" | MATCH "hello-from-snap"

tools/spread/load_snapcraft_rock

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+#!/bin/bash
+
+# load_snapcraft_rock: helper to load the Snapcraft rock into docker.
+# 
+# The rock is always loaded as "snapcraft-rock", regardless of supported base. 
+
+if stat ${PROJECT_PATH}/tests/*.rock 2>/dev/null; then
+  rockname=$(ls ${PROJECT_PATH}/tests/*.rock)
+  /snap/rockcraft/current/bin/skopeo --insecure-policy copy oci-archive:${rockname} docker-daemon:snapcraft-rock:latest
+else
+  echo "Expected a rock to exist in ${PROJECT_PATH}/tests/"
+  exit 1
+fi

tools/spread/run_snapcraft

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+#!/bin/bash
+
+# run_snapcraft: helper to run Snapcraft inside a container.
+
+# replace the SNAPCRAFT_BASE token with the correct base for our Snapcraft image
+sed --in-place=.bak "s/SNAPCRAFT_BASE/$SNAPCRAFT_BASE/" snap/snapcraft.yaml
+docker run --rm -v `pwd`:/project snapcraft-rock:latest "$@"