diff --git a/.gitignore b/.gitignore
index 0cd204c..d0f8788 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 node_modules
 .mcp-cli
 dist
+coverage/
diff --git a/tests/deno-open_test.ts b/tests/deno-open_test.ts
index d553fe0..b485a5b 100644
--- a/tests/deno-open_test.ts
+++ b/tests/deno-open_test.ts
@@ -96,4 +96,215 @@ describe("deno-open", () => {
     );
     assertSpyCalls(commandSpy, 1);
   });
+
+  it("calls the correct command on Linux", async () => {
+    // Mock Deno.Command implementation to return success
+    const mockOutput = {
+      success: true,
+      code: 0,
+      stdout: new Uint8Array(),
+      stderr: new Uint8Array(),
+    };
+    const mockCommandConstructor = () => ({ output: () => Promise.resolve(mockOutput) });
+    commandSpy = spy(mockCommandConstructor);
+    (Deno.Command as unknown) = commandSpy;
+
+    // Call open, specifying linux in options
+    const url = "https://example.com";
+    await open(url, { os: "linux" });
+
+    // Verify the spy was called with correct arguments
+    assertSpyCalls(commandSpy, 1);
+    assertEquals(commandSpy.calls[0].args[0], "xdg-open");
+    assertEquals(commandSpy.calls[0].args[1]?.args, [url]);
+  });
+
+  it("throws error for unsupported platform", async () => {
+    // Call open with an unsupported platform
+    const url = "https://example.com";
+    await assertRejects(
+      () => open(url, { os: "freebsd" }),
+      Error,
+      "Unsupported platform: freebsd"
+    );
+  });
+
+  it("uses specified app on macOS", async () => {
+    // Mock Deno.Command implementation to return success
+    const mockOutput = {
+      success: true,
+      code: 0,
+      stdout: new Uint8Array(),
+      stderr: new Uint8Array(),
+    };
+    const mockCommandConstructor = () => ({ output: () => Promise.resolve(mockOutput) });
+    commandSpy = spy(mockCommandConstructor);
+    (Deno.Command as unknown) = commandSpy;
+
+    // Call open with app option
+    const url = "https://example.com";
+    const app = "Safari";
+    await open(url, { os: "darwin", app: app });
+
+    // Verify the spy was called with correct arguments
+    assertSpyCalls(commandSpy, 1);
+    assertEquals(commandSpy.calls[0].args[0], "open");
+    assertEquals(commandSpy.calls[0].args[1]?.args, ["-a", app, url]);
+  });
+
+  it("uses specified app on Linux", async () => {
+    // Mock Deno.Command implementation to return success
+    const mockOutput = {
+      success: true,
+      code: 0,
+      stdout: new Uint8Array(),
+      stderr: new Uint8Array(),
+    };
+    const mockCommandConstructor = () => ({ output: () => Promise.resolve(mockOutput) });
+    commandSpy = spy(mockCommandConstructor);
+    (Deno.Command as unknown) = commandSpy;
+
+    // Call open with app option
+    const url = "https://example.com";
+    const app = "firefox";
+    await open(url, { os: "linux", app: app });
+
+    // Verify that it uses the app directly as the command
+    assertSpyCalls(commandSpy, 1);
+    assertEquals(commandSpy.calls[0].args[0], app);
+    assertEquals(commandSpy.calls[0].args[1]?.args, [url]);
+  });
+
+  it("handles wait option on macOS", async () => {
+    // Mock Deno.Command implementation to return success
+    const mockOutput = {
+      success: true,
+      code: 0,
+      stdout: new Uint8Array(),
+      stderr: new Uint8Array(),
+    };
+    const mockCommandConstructor = () => ({ output: () => Promise.resolve(mockOutput) });
+    commandSpy = spy(mockCommandConstructor);
+    (Deno.Command as unknown) = commandSpy;
+
+    // Call open with wait option
+    const url = "https://example.com";
+    await open(url, { os: "darwin", wait: true });
+
+    // Verify the spy was called with correct arguments
+    assertSpyCalls(commandSpy, 1);
+    assertEquals(commandSpy.calls[0].args[0], "open");
+    assertEquals(commandSpy.calls[0].args[1]?.args, ["-W", url]);
+  });
+
+  it("handles wait option on Windows", async () => {
+    // Mock Deno.Command implementation to return success
+    const mockOutput = {
+      success: true,
+      code: 0,
+      stdout: new Uint8Array(),
+      stderr: new Uint8Array(),
+    };
+    const mockCommandConstructor = () => ({ output: () => Promise.resolve(mockOutput) });
+    commandSpy = spy(mockCommandConstructor);
+    (Deno.Command as unknown) = commandSpy;
+
+    // Call open with wait option
+    const url = "https://example.com";
+    await open(url, { os: "windows", wait: true });
+
+    // Verify the spy was called with correct arguments
+    assertSpyCalls(commandSpy, 1);
+    assertEquals(commandSpy.calls[0].args[0], "cmd");
+    assertEquals(commandSpy.calls[0].args[1]?.args, ["/c", "start", '""', "/wait", url]);
+  });
+
+  it("handles background option on macOS", async () => {
+    // Mock Deno.Command implementation to return success
+    const mockOutput = {
+      success: true,
+      code: 0,
+      stdout: new Uint8Array(),
+      stderr: new Uint8Array(),
+    };
+    const mockCommandConstructor = () => ({ output: () => Promise.resolve(mockOutput) });
+    commandSpy = spy(mockCommandConstructor);
+    (Deno.Command as unknown) = commandSpy;
+
+    // Call open with background option
+    const url = "https://example.com";
+    await open(url, { os: "darwin", background: true });
+
+    // Verify the spy was called with correct arguments
+    assertSpyCalls(commandSpy, 1);
+    assertEquals(commandSpy.calls[0].args[0], "open");
+    assertEquals(commandSpy.calls[0].args[1]?.args, ["-g", url]);
+  });
+
+  it("escapes ampersands in URLs on Windows", async () => {
+    // Mock Deno.Command implementation to return success
+    const mockOutput = {
+      success: true,
+      code: 0,
+      stdout: new Uint8Array(),
+      stderr: new Uint8Array(),
+    };
+    const mockCommandConstructor = () => ({ output: () => Promise.resolve(mockOutput) });
+    commandSpy = spy(mockCommandConstructor);
+    (Deno.Command as unknown) = commandSpy;
+
+    // Call open with URL containing ampersands
+    const url = "https://example.com?param1=value1&param2=value2";
+    await open(url, { os: "windows" });
+
+    // Verify the spy was called with escaped ampersands
+    assertSpyCalls(commandSpy, 1);
+    assertEquals(commandSpy.calls[0].args[0], "cmd");
+    assertEquals(
+      commandSpy.calls[0].args[1]?.args,
+      ["/c", "start", '""', "https://example.com?param1=value1^&param2=value2"]
+    );
+  });
+
+  it("throws error when command not found", async () => {
+    // Mock Deno.Command to throw NotFound error
+    const mockCommandConstructor = () => {
+      throw new Deno.errors.NotFound();
+    };
+    commandSpy = spy(mockCommandConstructor);
+    (Deno.Command as unknown) = commandSpy;
+
+    // Call open and expect it to throw
+    const url = "https://example.com";
+    await assertRejects(
+      () => open(url, { os: "darwin" }),
+      Error,
+      `Failed to open "${url}": Command not found: open`
+    );
+    assertSpyCalls(commandSpy, 1);
+  });
+
+  it("includes stdout in error message when available", async () => {
+    // Mock Deno.Command to return failure with stdout
+    const stderrOutput = new TextEncoder().encode("Error details");
+    const stdoutOutput = new TextEncoder().encode("Additional info");
+    const mockOutput = {
+      success: false,
+      code: 1,
+      stdout: stdoutOutput,
+      stderr: stderrOutput,
+    };
+    const mockCommandConstructor = () => ({ output: () => Promise.resolve(mockOutput) });
+    commandSpy = spy(mockCommandConstructor);
+    (Deno.Command as unknown) = commandSpy;
+
+    // Call open and expect it to throw with stdout included in error
+    const url = "https://example.com";
+    await assertRejects(
+      () => open(url, { os: "darwin" }),
+      Error,
+      `Failed to open "${url}". Command "open ${url}" exited with code 1.\nStderr: Error details\nStdout: Additional info`
+    );
+    assertSpyCalls(commandSpy, 1);
+  });
 });
diff --git a/tests/mcp-auth-config_test.ts b/tests/mcp-auth-config_test.ts
index 1ca81e6..8f7aaee 100644
--- a/tests/mcp-auth-config_test.ts
+++ b/tests/mcp-auth-config_test.ts
@@ -1,15 +1,26 @@
 import {
   assertEquals,
   assertStringIncludes,
+  assertRejects,
 } from "std/assert/mod.ts";
-import { describe, it, afterEach } from "std/testing/bdd.ts";
+import { describe, it, afterEach, beforeEach } from "std/testing/bdd.ts";
 import {
   getConfigDir,
   getConfigFilePath,
+  ensureConfigDir,
+  createLockfile,
+  checkLockfile,
+  deleteLockfile,
+  readJsonFile,
+  writeJsonFile,
+  deleteConfigFile,
+  readTextFile,
+  writeTextFile,
 } from "../src/lib/mcp-auth-config.ts";
 import { MCP_REMOTE_VERSION } from "../src/lib/utils.ts";
 import * as path from "node:path";
 import * as os from "node:os";
+import { assertSpyCalls, spy } from "std/testing/mock.ts";
 
 describe("mcp-auth-config", () => {
   describe("getConfigDir", () => {
@@ -61,4 +72,55 @@ describe("mcp-auth-config", () => {
       assertEquals(filePath, expectedPath);
     });
   });
+
+  describe("ensureConfigDir", () => {
+    it("creates directory when it doesn't exist", async () => {
+      // Basic test without spies
+      await ensureConfigDir();
+      // If it doesn't throw, we're good
+      assertEquals(true, true);
+    });
+  });
+
+  describe("lockfile functions", () => {
+    const testHash = "testhash123";
+    const testPort = 12345;
+    const testPid = 67890;
+
+    it("can create and check lockfiles", async () => {
+      // Just test basic functionality without spies
+      await createLockfile(testHash, testPid, testPort);
+
+      const lockfile = await checkLockfile(testHash);
+
+      // Only check that data is correctly returned, not implementation details
+      assertEquals(lockfile?.pid, testPid);
+      assertEquals(lockfile?.port, testPort);
+
+      // Clean up
+      await deleteLockfile(testHash);
+    });
+  });
+
+  describe("file operations", () => {
+    const testHash = "testhash987";
+    const testFilename = "test-fileops.json";
+    const testData = { key: "value" };
+
+    it("writes and reads JSON files", async () => {
+      await writeJsonFile(testHash, testFilename, testData);
+
+      const parseFunc = {
+        parseAsync: (data: unknown) => {
+          return Promise.resolve(data);
+        },
+      };
+
+      const result = await readJsonFile(testHash, testFilename, parseFunc);
+      assertEquals((result as any)?.key, testData.key);
+
+      // Clean up
+      await deleteConfigFile(testHash, testFilename);
+    });
+  });
 });
diff --git a/tests/utils_test.ts b/tests/utils_test.ts
index cb38aaa..fb6efb2 100644
--- a/tests/utils_test.ts
+++ b/tests/utils_test.ts
@@ -1,7 +1,25 @@
-import { assertEquals, assertMatch } from "std/assert/mod.ts";
-import { getServerUrlHash, log, MCP_REMOTE_VERSION } from "../src/lib/utils.ts";
+import { assertEquals, assertMatch, assertRejects } from "std/assert/mod.ts";
+import {
+  getServerUrlHash,
+  log,
+  MCP_REMOTE_VERSION,
+  findAvailablePort,
+  mcpProxy,
+  setupSignalHandlers,
+  parseCommandLineArgs
+} from "../src/lib/utils.ts";
 import { afterEach, beforeEach, describe, it } from "std/testing/bdd.ts";
 import { assertSpyCalls, spy, type MethodSpy } from "std/testing/mock.ts";
+import { EventEmitter } from "node:events";
+import net from "node:net";
+import type { Transport } from "npm:@modelcontextprotocol/sdk/shared/transport.js";
+
+// Define mock server type
+interface MockServer {
+  listen: (port: number, callback: () => void) => MockServer;
+  close: (callback: () => void) => MockServer;
+  on: (event: string, callback: () => void) => MockServer;
+}
 
 describe("utils", () => {
   describe("getServerUrlHash", () => {
@@ -74,4 +92,152 @@ describe("utils", () => {
       assertMatch(MCP_REMOTE_VERSION, /^\d+\.\d+\.\d+$/);
     });
   });
+
+  describe("findAvailablePort", () => {
+    let originalNetCreateServer: typeof net.createServer;
+    let serverListenSpy: MethodSpy<MockServer, [port: number, callback: () => void], MockServer>;
+    let serverCloseSpy: MethodSpy<MockServer, [callback: () => void], MockServer>;
+
+    beforeEach(() => {
+      // Mock server behavior
+      originalNetCreateServer = net.createServer;
+
+      // Mock a server object
+      const mockServer: MockServer = {
+        listen: (port: number, callback: () => void) => {
+          // Call the callback to simulate server starting
+          callback();
+          return mockServer;
+        },
+        close: (callback: () => void) => {
+          // Call the callback to simulate server closing
+          callback();
+          return mockServer;
+        },
+        on: (_event: string, _callback: () => void) => {
+          return mockServer;
+        },
+      };
+
+      // Create spies on the mock server methods
+      serverListenSpy = spy(mockServer, "listen");
+      serverCloseSpy = spy(mockServer, "close");
+
+      // Mock the net.createServer
+      net.createServer = () => mockServer as unknown as net.Server;
+    });
+
+    afterEach(() => {
+      // Restore original net.createServer
+      net.createServer = originalNetCreateServer;
+
+      // Clean up spies
+      serverListenSpy.restore();
+      serverCloseSpy.restore();
+    });
+
+    it("finds an available port using the preferred port when it's available", async () => {
+      const preferredPort = 8080;
+      const port = await findAvailablePort(preferredPort);
+
+      assertEquals(port, preferredPort);
+      assertSpyCalls(serverListenSpy, 1);
+      assertSpyCalls(serverCloseSpy, 1);
+    });
+
+    it("finds an available port automatically when no preference is given", async () => {
+      const port = await findAvailablePort();
+
+      assertEquals(typeof port, "number");
+      assertSpyCalls(serverListenSpy, 1);
+      assertSpyCalls(serverCloseSpy, 1);
+    });
+  });
+
+  describe("parseCommandLineArgs", () => {
+    it("parses valid arguments", async () => {
+      const args = ["--server", "https://example.com", "--port", "8080"];
+      const defaultPort = 3000;
+      const usage = "Usage: mcp-remote --server <url> [--port <port>]";
+
+      const result = await parseCommandLineArgs(args, defaultPort, usage);
+
+      assertEquals(result.serverUrl, "https://example.com");
+      assertEquals(result.callbackPort, 8080);
+    });
+
+    it("uses default port if not specified", async () => {
+      const args = ["--server", "https://example.com"];
+      const defaultPort = 3000;
+      const usage = "Usage: mcp-remote --server <url> [--port <port>]";
+
+      const result = await parseCommandLineArgs(args, defaultPort, usage);
+
+      assertEquals(result.serverUrl, "https://example.com");
+      assertEquals(result.callbackPort, defaultPort);
+    });
+
+    it("enforces required server URL", async () => {
+      const args: string[] = [];
+      const defaultPort = 3000;
+      const usage = "Usage: mcp-remote --server <url> [--port <port>]";
+
+      await assertRejects(
+        async () => {
+          await parseCommandLineArgs(args, defaultPort, usage);
+        },
+        Error,
+        "Server URL is required"
+      );
+    });
+
+    it("handles format errors in server URL", async () => {
+      const args = ["--server", "not-a-url"];
+      const defaultPort = 3000;
+      const usage = "Usage: mcp-remote --server <url> [--port <port>]";
+
+      await assertRejects(
+        async () => {
+          await parseCommandLineArgs(args, defaultPort, usage);
+        },
+        Error
+      );
+    });
+
+    it("handles invalid port numbers", async () => {
+      const args = ["--server", "https://example.com", "--port", "invalid"];
+      const defaultPort = 3000;
+      const usage = "Usage: mcp-remote --server <url> [--port <port>]";
+
+      await assertRejects(
+        async () => {
+          await parseCommandLineArgs(args, defaultPort, usage);
+        },
+        Error
+      );
+    });
+  });
+
+  describe("setupSignalHandlers", () => {
+    it("sets up handlers for SIGINT and SIGTERM", () => {
+      // Create spies for process.on
+      const processSpy = spy(Deno, "addSignalListener");
+
+      // Mock cleanup function
+      const cleanup = spy(() => Promise.resolve());
+
+      // Call the function
+      setupSignalHandlers(cleanup);
+
+      // Verify signal handlers are set
+      assertSpyCalls(processSpy, 2);
+      assertEquals(processSpy.calls[0].args[0], "SIGINT");
+      assertEquals(typeof processSpy.calls[0].args[1], "function");
+      assertEquals(processSpy.calls[1].args[0], "SIGTERM");
+      assertEquals(typeof processSpy.calls[1].args[1], "function");
+
+      // Restore spy
+      processSpy.restore();
+    });
+  });
 });