Add script to verify exercises in Docker (#188)

TRACK_README.md

@@ -11,6 +11,18 @@ This command will iterate over all exercises and check to see if their exemplar/
 
 To test a single exercise, run `./bin/verify-exercises <exercise-slug>`.
 
+### Using Docker
+
+If your track has a working [test runner](https://exercism.org/docs/building/tooling/test-runners), the `./bin/verify-exercises-in-docker` script can also be used to test all exercises.
+This script pulls (_downloads_) the test runner's [Docker image](https://exercism.org/docs/building/tooling/test-runners/docker) and then uses Docker to run that image to test an exercise.
+
+```exercism/note
+The main benefit of this approach is that it best mimics how exercises are tested in production (on the website).
+Another benefit is that you don't have to install track-specific dependencies (e.g. an SDK) locally, you just need Docker installed.
+```
+
+To test a single exercise, run `./bin/verify-exercises-in-docker <exercise-slug>`.
+
 ### Track linting
 
 [`configlet`](https://exercism.org/docs/building/configlet) is an Exercism-wide tool for working with tracks. You can download it by running:

bin/bootstrap

@@ -66,6 +66,7 @@ end
   "config.json",
   "README.md",
   "CHECKLIST.md",
+  File.join("bin", "verify-exercises-in-docker"),
   File.join("docs", "config.json")
 ].each do |name|
   f = File.join(dir, name)

bin/verify-exercises

@@ -73,14 +73,21 @@ verify_exercise() {
     )
 }
 
-exercise_slug="${1:-*}"
+verify_exercises() {
+    local exercise_slug
+
+    exercise_slug="${1}"
+
+    shopt -s nullglob
+    count=0
+    for exercise_dir in ./exercises/{concept,practice}/${exercise_slug}/; do
+        if [[ -d "${exercise_dir}" ]]; then
+            verify_exercise "${exercise_dir}"
+            ((++count))
+        fi
+    done
+    ((count > 0)) || die 'no matching exercises found!'
+}
 
-shopt -s nullglob
-count=0
-for exercise_dir in ./exercises/{concept,practice}/${exercise_slug}/; do
-    if [[ -d "${exercise_dir}" ]]; then
-        verify_exercise "${exercise_dir}"
-        ((++count))
-    fi
-done
-((count > 0)) || die 'no matching exercises found!'
+exercise_slug="${1:-*}"
+verify_exercises "${exercise_slug}"

bin/verify-exercises-in-docker

@@ -0,0 +1,89 @@
+#!/usr/bin/env bash
+
+# Synopsis:
+# Verify that each exercise's example/exemplar solution passes the tests
+# using the track's test runner Docker image.
+# You can either verify all exercises or a single exercise.
+
+# Example: verify all exercises in Docker
+# bin/verify-exercises-in-docker
+
+# Example: verify single exercise in Docker
+# bin/verify-exercises-in-docker two-fer
+
+set -eo pipefail
+
+die() { echo "$*" >&2; exit 1; }
+
+required_tool() {
+    command -v "${1}" >/dev/null 2>&1 ||
+        die "${1} is required but not installed. Please install it and make sure it's in your PATH."
+}
+
+required_tool docker
+
+copy_example_or_examplar_to_solution() {
+    jq -c '[.files.solution, .files.exemplar // .files.example] | transpose | map({src: .[1], dst: .[0]}) | .[]' .meta/config.json \
+    | while read -r src_and_dst; do
+        cp "$(jq -r '.src' <<< "${src_and_dst}")" "$(jq -r '.dst' <<< "${src_and_dst}")"
+    done
+}
+
+pull_docker_image() {
+    docker pull exercism/{{SLUG}}-test-runner
+}
+
+run_tests() {
+    local slug
+    slug="${1}"
+
+    docker run \
+        --rm \
+        --network none \
+        --read-only \
+        --mount type=bind,src="${PWD}",dst=/solution \
+        --mount type=bind,src="${PWD}",dst=/output \
+        --mount type=tmpfs,dst=/tmp \
+        exercism/{{SLUG}}-test-runner "${slug}" /solution /output
+    jq -e '.status == "pass"' "${PWD}/results.json" >/dev/null 2>&1
+}
+
+verify_exercise() {
+    local dir
+    local slug
+    local tmp_dir
+    dir=$(realpath "${1}")
+    slug=$(basename "${dir}")
+    tmp_dir=$(mktemp -d -t "exercism-verify-${slug}-XXXXX")
+
+    echo "Verifying ${slug} exercise..."
+
+    (
+        trap 'rm -rf "$tmp_dir"' EXIT    # remove tempdir when subshell ends
+        cp -r "${dir}/." "${tmp_dir}"
+        cd "${tmp_dir}"
+
+        copy_example_or_examplar_to_solution
+        run_tests "${slug}"
+    )
+}
+
+verify_exercises() {
+    local exercise_slug
+    exercise_slug="${1}"
+
+    shopt -s nullglob
+    count=0
+    for exercise_dir in ./exercises/{concept,practice}/${exercise_slug}/; do
+        if [[ -d "${exercise_dir}" ]]; then
+            verify_exercise "${exercise_dir}"
+            ((++count))
+        fi
+    done
+    ((count > 0)) || die 'no matching exercises found!'
+}
+
+pull_docker_image
+
+exercise_slug="${1:-*}"
+verify_exercises "${exercise_slug}"