Initial Dockge image update checker

test/image-ref.test.js

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+import assert from "node:assert/strict";
+import { test } from "node:test";
+import { digestMatchesRepoDigests, parseImageRef } from "../src/image-ref.js";
+
+test("parses Docker Hub shorthand image references", () => {
+  assert.deepEqual(parseImageRef("nginx:1.27"), {
+    original: "nginx:1.27",
+    registry: "registry-1.docker.io",
+    repository: "library/nginx",
+    tag: "1.27",
+    registryRef: "registry-1.docker.io/library/nginx:1.27",
+    repositoryRef: "registry-1.docker.io/library/nginx",
+  });
+});
+
+test("parses custom registry image references", () => {
+  assert.deepEqual(parseImageRef("ghcr.io/example/app:main").registryRef, "ghcr.io/example/app:main");
+});
+
+test("defaults missing tags to latest", () => {
+  assert.equal(parseImageRef("redis").tag, "latest");
+});
+
+test("matches remote digests against repo digests", () => {
+  const imageRef = parseImageRef("nginx:latest");
+  assert.equal(digestMatchesRepoDigests("sha256:abc", ["registry-1.docker.io/library/nginx@sha256:abc"], imageRef), true);
+  assert.equal(digestMatchesRepoDigests("sha256:def", ["registry-1.docker.io/library/nginx@sha256:abc"], imageRef), false);
+});