diff --git a/src/tests/utils/markdownEditorUtils.test.ts b/src/tests/utils/markdownEditorUtils.test.ts
new file mode 100644
index 00000000..e794a2f6
--- /dev/null
+++ b/src/tests/utils/markdownEditorUtils.test.ts
@@ -0,0 +1,202 @@
+import {
+  parseLine,
+  detectPrefix,
+  allLinesHavePrefix,
+  createLineEditRange,
+} from "../../utils/markdownEditorUtils";
+
+describe("markdownEditorUtils", () => {
+  describe("parseLine", () => {
+    it("should return empty whitespace for line with no leading spaces", () => {
+      const result = parseLine("Hello World");
+      expect(result).toEqual({
+        leadingWhitespace: "",
+        content: "Hello World",
+      });
+    });
+
+    it("should extract leading spaces", () => {
+      const result = parseLine("  Hello");
+      expect(result).toEqual({
+        leadingWhitespace: "  ",
+        content: "Hello",
+      });
+    });
+
+    it("should extract leading tabs", () => {
+      const result = parseLine("\t\tHello");
+      expect(result).toEqual({
+        leadingWhitespace: "\t\t",
+        content: "Hello",
+      });
+    });
+
+    it("should handle mixed whitespace", () => {
+      const result = parseLine(" \t Hello");
+      expect(result).toEqual({
+        leadingWhitespace: " \t ",
+        content: "Hello",
+      });
+    });
+
+    it("should handle empty line", () => {
+      const result = parseLine("");
+      expect(result).toEqual({
+        leadingWhitespace: "",
+        content: "",
+      });
+    });
+
+    it("should handle line with only whitespace", () => {
+      const result = parseLine("   ");
+      expect(result).toEqual({
+        leadingWhitespace: "   ",
+        content: "",
+      });
+    });
+  });
+
+  describe("detectPrefix", () => {
+    it("should return undefined matched when no prefix found", () => {
+      const result = detectPrefix("Hello World", ["#", "##", "###"]);
+      expect(result).toEqual({
+        matched: undefined,
+        stripped: "Hello World",
+      });
+    });
+
+    it("should detect single hash heading prefix", () => {
+      const result = detectPrefix("# Hello", ["#", "##", "###"]);
+      expect(result).toEqual({
+        matched: "#",
+        stripped: "Hello",
+      });
+    });
+
+    it("should detect double hash heading prefix", () => {
+      const result = detectPrefix("## Hello", ["#", "##", "###"]);
+      expect(result).toEqual({
+        matched: "##",
+        stripped: "Hello",
+      });
+    });
+
+    it("should detect triple hash heading prefix", () => {
+      const result = detectPrefix("### Hello", ["#", "##", "###"]);
+      expect(result).toEqual({
+        matched: "###",
+        stripped: "Hello",
+      });
+    });
+
+    it("should detect unordered list prefix", () => {
+      const result = detectPrefix("- Item", ["-"]);
+      expect(result).toEqual({
+        matched: "-",
+        stripped: "Item",
+      });
+    });
+
+    it("should handle prefix with no content after it", () => {
+      const result = detectPrefix("#", ["#", "##"]);
+      expect(result).toEqual({
+        matched: "#",
+        stripped: "",
+      });
+    });
+
+    it("should not match prefix that is not in the list", () => {
+      const result = detectPrefix("* Item", ["-"]);
+      expect(result).toEqual({
+        matched: undefined,
+        stripped: "* Item",
+      });
+    });
+
+    it("should handle content with leading spaces before prefix", () => {
+      const result = detectPrefix("  # Hello", ["#", "##"]);
+      expect(result).toEqual({
+        matched: "#",
+        stripped: "Hello",
+      });
+    });
+
+    it("should not match when prefix is part of word", () => {
+      const result = detectPrefix("#hashtag", ["#"]);
+      expect(result).toEqual({
+        matched: undefined,
+        stripped: "#hashtag",
+      });
+    });
+  });
+
+  describe("allLinesHavePrefix", () => {
+    it("should return true when all lines have the same prefix", () => {
+      const lines = ["# Hello", "# World", "# Test"];
+      const result = allLinesHavePrefix(lines, "#", ["#", "##", "###"]);
+      expect(result).toBe(true);
+    });
+
+    it("should return false when lines have different prefixes", () => {
+      const lines = ["# Hello", "## World", "# Test"];
+      const result = allLinesHavePrefix(lines, "#", ["#", "##", "###"]);
+      expect(result).toBe(false);
+    });
+
+    it("should return false when some lines have no prefix", () => {
+      const lines = ["# Hello", "World", "# Test"];
+      const result = allLinesHavePrefix(lines, "#", ["#", "##", "###"]);
+      expect(result).toBe(false);
+    });
+
+    it("should handle single line", () => {
+      const lines = ["# Hello"];
+      const result = allLinesHavePrefix(lines, "#", ["#", "##", "###"]);
+      expect(result).toBe(true);
+    });
+
+    it("should handle lines with leading whitespace", () => {
+      const lines = ["  # Hello", "  # World"];
+      const result = allLinesHavePrefix(lines, "#", ["#", "##", "###"]);
+      expect(result).toBe(true);
+    });
+
+    it("should return true for empty array", () => {
+      const lines: string[] = [];
+      const result = allLinesHavePrefix(lines, "#", ["#", "##", "###"]);
+      expect(result).toBe(true);
+    });
+  });
+
+  describe("createLineEditRange", () => {
+    it("should create correct range for line 1", () => {
+      const result = createLineEditRange(1, 10);
+      expect(result).toEqual({
+        startLineNumber: 1,
+        startColumn: 1,
+        endLineNumber: 1,
+        endColumn: 11,
+      });
+    });
+
+    it("should create correct range for arbitrary line", () => {
+      const result = createLineEditRange(5, 20);
+      expect(result).toEqual({
+        startLineNumber: 5,
+        startColumn: 1,
+        endLineNumber: 5,
+        endColumn: 21,
+      });
+    });
+
+    it("should handle zero-length line", () => {
+      const result = createLineEditRange(3, 0);
+      expect(result).toEqual({
+        startLineNumber: 3,
+        startColumn: 1,
+        endLineNumber: 3,
+        endColumn: 1,
+      });
+    });
+  });
+});
diff --git a/src/utils/testing/__mocks__/monaco-editor.ts b/src/utils/testing/__mocks__/monaco-editor.ts
new file mode 100644
index 00000000..fe513ce1
--- /dev/null
+++ b/src/utils/testing/__mocks__/monaco-editor.ts
@@ -0,0 +1,22 @@
+/**
+ * Mock for monaco-editor module used in tests
+ * This allows testing utilities that import Monaco types without loading the full editor
+ */
+
+export class Selection {
+  constructor(
+    public startLineNumber: number,
+    public startColumn: number,
+    public endLineNumber: number,
+    public endColumn: number
+  ) {}
+}
+
+export const editor = {};
+
+export interface IRange {
+  startLineNumber: number;
+  startColumn: number;
+  endLineNumber: number;
+  endColumn: number;
+}
diff --git a/vite.config.ts b/vite.config.ts
index 873b9d67..1c1a8feb 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -1,3 +1,4 @@
+import { fileURLToPath } from "node:url";
 import { defineConfig as defineViteConfig, mergeConfig } from "vite";
 import { defineConfig as defineVitestConfig, configDefaults } from "vitest/config";
 import react from "@vitejs/plugin-react";
@@ -23,6 +24,12 @@ const vitestConfig = defineVitestConfig({
     environment: "jsdom",
     setupFiles: "./src/utils/testing/setup.ts",
     exclude: [...configDefaults.exclude, "**/e2e/**"],
+    deps: {
+      inline: ["monaco-editor"],
+    },
+    alias: {
+      "monaco-editor": fileURLToPath(new URL("./src/utils/testing/__mocks__/monaco-editor.ts", import.meta.url)),
+    },
   },
 });