diff --git a/test/obsidian-plugin.test.js b/test/obsidian-plugin.test.js
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+++ b/test/obsidian-plugin.test.js
@@ -0,0 +1,162 @@
+import test from "node:test";
+import assert from "node:assert/strict";
+import fs from "node:fs";
+import path from "node:path";
+
+const pluginPath = path.resolve("/home/venus/Documents/Notes/.obsidian/plugins/blog-publisher/main.js");
+
+// Pure helper function to be tested and exported/used by plugin
+export function insertOrUpdateFrontmatterProperty(content, key, value) {
+  if (typeof content !== "string") return "";
+
+  const fmRegex = /^---\r?\n([\s\S]*?)\r?\n---/;
+  const match = content.match(fmRegex);
+
+  if (match) {
+    let fmBlock = match[1];
+    const keyRegex = new RegExp(`^${key}:.*$`, "m");
+
+    if (value === null || value === undefined) {
+      // Remove property if value is null
+      fmBlock = fmBlock.replace(new RegExp(`^${key}:.*\\r?\\n?`, "m"), "");
+    } else if (keyRegex.test(fmBlock)) {
+      // Replace existing property
+      fmBlock = fmBlock.replace(keyRegex, `${key}: "${value}"`);
+    } else {
+      // Append property to frontmatter
+      fmBlock = `${fmBlock}\n${key}: "${value}"`;
+    }
+
+    return content.replace(fmRegex, `---\n${fmBlock.trim()}\n---`);
+  } else if (value) {
+    return `---\n${key}: "${value}"\n---\n\n${content}`;
+  }
+
+  return content;
+}
+
+export function computePublicUrl(serverUrl, postPath) {
+  const base = (serverUrl || "").replace(/\/+$/, "");
+  const p = (postPath || "").startsWith("/") ? postPath : `/${postPath || ""}`;
+  return `${base}${p}`;
+}
+
+test("Obsidian Plugin: computePublicUrl normalizes slashes correctly", () => {
+  assert.equal(
+    computePublicUrl("https://riverrooks.dev", "/posts/test-note/"),
+    "https://riverrooks.dev/posts/test-note/"
+  );
+  assert.equal(
+    computePublicUrl("https://riverrooks.dev/", "/posts/test-note/"),
+    "https://riverrooks.dev/posts/test-note/"
+  );
+  assert.equal(
+    computePublicUrl("https://riverrooks.dev///", "posts/test-note/"),
+    "https://riverrooks.dev/posts/test-note/"
+  );
+  assert.equal(
+    computePublicUrl("http://localhost:8080", "/posts/test-note/"),
+    "http://localhost:8080/posts/test-note/"
+  );
+});
+
+test("Obsidian Plugin: insertOrUpdateFrontmatterProperty adds public-url when missing", () => {
+  const original = `---
+title: "Sample Note"
+date: 2026-09-23
+publish: true
+---
+
+# Content here`;
+
+  const updated = insertOrUpdateFrontmatterProperty(
+    original,
+    "public-url",
+    "https://riverrooks.dev/posts/sample-note/"
+  );
+
+  assert.match(
+    updated,
+    /public-url:\s*"https:\/\/riverrooks\.dev\/posts\/sample-note\/"/,
+    "Must insert public-url into frontmatter"
+  );
+  assert.match(updated, /title:\s*"Sample Note"/, "Preserves title");
+  assert.match(updated, /publish:\s*true/, "Preserves publish flag");
+  assert.match(updated, /# Content here/, "Preserves body content");
+});
+
+test("Obsidian Plugin: insertOrUpdateFrontmatterProperty updates existing public-url", () => {
+  const original = `---
+title: "Updated Note"
+date: 2026-09-23
+public-url: "https://old.domain/posts/sample-note/"
+---
+
+Body`;
+
+  const updated = insertOrUpdateFrontmatterProperty(
+    original,
+    "public-url",
+    "https://riverrooks.dev/posts/updated-note/"
+  );
+
+  assert.match(
+    updated,
+    /public-url:\s*"https:\/\/riverrooks\.dev\/posts\/updated-note\/"/,
+    "Must update public-url to new URL"
+  );
+  assert.doesNotMatch(
+    updated,
+    /old\.domain/,
+    "Old URL must be replaced"
+  );
+});
+
+test("Obsidian Plugin: insertOrUpdateFrontmatterProperty removes public-url on unpublish", () => {
+  const original = `---
+title: "Unpublished Note"
+date: 2026-09-23
+public-url: "https://riverrooks.dev/posts/sample-note/"
+---
+
+Body`;
+
+  const updated = insertOrUpdateFrontmatterProperty(original, "public-url", null);
+
+  assert.doesNotMatch(updated, /public-url:/, "Must remove public-url when value is null");
+  assert.match(updated, /title:\s*"Unpublished Note"/, "Preserves other frontmatter");
+});
+
+test("Obsidian Plugin: Adversarial edge cases for frontmatter property insertion", () => {
+  // 1. Empty content
+  assert.equal(insertOrUpdateFrontmatterProperty("", "public-url", "https://url"), "---\npublic-url: \"https://url\"\n---\n\n");
+  // 2. Non-string inputs
+  assert.equal(insertOrUpdateFrontmatterProperty(null, "public-url", "https://url"), "");
+  assert.equal(insertOrUpdateFrontmatterProperty(undefined, "public-url", "https://url"), "");
+  // 3. Note without frontmatter
+  const plain = "# Just a header\nSome text.";
+  const result = insertOrUpdateFrontmatterProperty(plain, "public-url", "https://url");
+  assert.match(result, /^---\npublic-url:\s*"https:\/\/url"\n---/);
+});
+
+test("Obsidian Plugin: main.js in vault includes public-url insertion and recursion guard", () => {
+  assert.ok(fs.existsSync(pluginPath), `Plugin main.js must exist at ${pluginPath}`);
+  const pluginContent = fs.readFileSync(pluginPath, "utf-8");
+
+  // 1. Must handle public-url
+  assert.match(pluginContent, /public-url/i, "main.js must reference 'public-url'");
+
+  // 2. Must guard against infinite loops during frontmatter updates
+  assert.match(
+    pluginContent,
+    /isUpdatingFrontmatter/i,
+    "main.js must maintain a guard to prevent metadataCache recursion loops"
+  );
+
+  // 3. Must use processFrontMatter or frontmatter updater
+  assert.match(
+    pluginContent,
+    /processFrontMatter|updateFrontmatter/i,
+    "main.js must implement frontmatter updating logic"
+  );
+});