diff --git a/deno.json b/deno.json
index b61140f..9112729 100644
--- a/deno.json
+++ b/deno.json
@@ -1,12 +1,14 @@
 {
   "imports": {
-    "@std/cli": "jsr:@std/cli@^1.0.27",
-    "@std/fs": "jsr:@std/fs@^1.0.22",
-    "@std/path": "jsr:@std/path@^1.1.4",
+    // Using pinned versions due to JSR connectivity issues in CI environment
+    "@std/cli": "https://deno.land/std@0.224.0/cli/mod.ts",
+    "@std/fs": "https://deno.land/std@0.224.0/fs/mod.ts",
+    "@std/path": "https://deno.land/std@0.224.0/path/mod.ts",
     "sharp": "npm:sharp@^0.34.5"
   },
   "tasks": {
-    "compile": "deno compile --allow-all main.ts"
+    "compile": "deno compile --allow-all main.ts",
+    "test": "deno test --allow-all --unsafely-ignore-certificate-errors"
   },
   "version": "0.0.1"
 }
diff --git a/deno.lock b/deno.lock
index 52e04a2..b87e099 100644
--- a/deno.lock
+++ b/deno.lock
@@ -1,45 +1,10 @@
 {
   "version": "5",
   "specifiers": {
-    "jsr:@std/cli@*": "1.0.27",
-    "jsr:@std/cli@^1.0.27": "1.0.27",
-    "jsr:@std/fmt@^1.0.9": "1.0.9",
-    "jsr:@std/fs@*": "1.0.22",
-    "jsr:@std/fs@^1.0.22": "1.0.22",
-    "jsr:@std/internal@^1.0.12": "1.0.12",
-    "jsr:@std/path@^1.1.4": "1.1.4",
     "npm:@imagemagick/magick-wasm@0.0.31": "0.0.31",
     "npm:@types/node@*": "24.2.0",
     "npm:sharp@~0.34.5": "0.34.5"
   },
-  "jsr": {
-    "@std/cli@1.0.27": {
-      "integrity": "eba97edd0891871a7410e835dd94b3c260c709cca5983df2689c25a71fbe04de",
-      "dependencies": [
-        "jsr:@std/fmt",
-        "jsr:@std/internal"
-      ]
-    },
-    "@std/fmt@1.0.9": {
-      "integrity": "2487343e8899fb2be5d0e3d35013e54477ada198854e52dd05ed0422eddcabe0"
-    },
-    "@std/fs@1.0.22": {
-      "integrity": "de0f277a58a867147a8a01bc1b181d0dfa80bfddba8c9cf2bacd6747bcec9308",
-      "dependencies": [
-        "jsr:@std/internal",
-        "jsr:@std/path"
-      ]
-    },
-    "@std/internal@1.0.12": {
-      "integrity": "972a634fd5bc34b242024402972cd5143eac68d8dffaca5eaa4dba30ce17b027"
-    },
-    "@std/path@1.1.4": {
-      "integrity": "1d2d43f39efb1b42f0b1882a25486647cb851481862dc7313390b2bb044314b5",
-      "dependencies": [
-        "jsr:@std/internal"
-      ]
-    }
-  },
   "npm": {
     "@emnapi/runtime@1.8.1": {
       "integrity": "sha512-mehfKSMWjjNol8659Z8KxEMrdSJDDot5SXMq00dM8BN4o+CLNXQ0xH2V7EchNHV4RmbZLmmPdEaXZc5H2FXmDg==",
@@ -261,6 +226,141 @@
     }
   },
   "remote": {
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+    "https://deno.land/std@0.224.0/assert/assert.ts": "09d30564c09de846855b7b071e62b5974b001bb72a4b797958fe0660e7849834",
+    "https://deno.land/std@0.224.0/assert/assert_almost_equals.ts": "9e416114322012c9a21fa68e187637ce2d7df25bcbdbfd957cd639e65d3cf293",
+    "https://deno.land/std@0.224.0/assert/assert_array_includes.ts": "14c5094471bc8e4a7895fc6aa5a184300d8a1879606574cb1cd715ef36a4a3c7",
+    "https://deno.land/std@0.224.0/assert/assert_equals.ts": "3bbca947d85b9d374a108687b1a8ba3785a7850436b5a8930d81f34a32cb8c74",
+    "https://deno.land/std@0.224.0/assert/assert_exists.ts": "43420cf7f956748ae6ed1230646567b3593cb7a36c5a5327269279c870c5ddfd",
+    "https://deno.land/std@0.224.0/assert/assert_false.ts": "3e9be8e33275db00d952e9acb0cd29481a44fa0a4af6d37239ff58d79e8edeff",
+    "https://deno.land/std@0.224.0/assert/assert_greater.ts": "5e57b201fd51b64ced36c828e3dfd773412c1a6120c1a5a99066c9b261974e46",
+    "https://deno.land/std@0.224.0/assert/assert_greater_or_equal.ts": "9870030f997a08361b6f63400273c2fb1856f5db86c0c3852aab2a002e425c5b",
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+    "https://deno.land/std@0.224.0/path/posix/is_glob.ts": "8a8b08c08bf731acf2c1232218f1f45a11131bc01de81e5f803450a5914434b9",
+    "https://deno.land/std@0.224.0/path/posix/join.ts": "7fc2cb3716aa1b863e990baf30b101d768db479e70b7313b4866a088db016f63",
+    "https://deno.land/std@0.224.0/path/posix/join_globs.ts": "a9475b44645feddceb484ee0498e456f4add112e181cb94042cdc6d47d1cdd25",
+    "https://deno.land/std@0.224.0/path/posix/mod.ts": "2301fc1c54a28b349e20656f68a85f75befa0ee9b6cd75bfac3da5aca9c3f604",
+    "https://deno.land/std@0.224.0/path/posix/normalize.ts": "baeb49816a8299f90a0237d214cef46f00ba3e95c0d2ceb74205a6a584b58a91",
+    "https://deno.land/std@0.224.0/path/posix/normalize_glob.ts": "9c87a829b6c0f445d03b3ecadc14492e2864c3ebb966f4cea41e98326e4435c6",
+    "https://deno.land/std@0.224.0/path/posix/parse.ts": "09dfad0cae530f93627202f28c1befa78ea6e751f92f478ca2cc3b56be2cbb6a",
+    "https://deno.land/std@0.224.0/path/posix/relative.ts": "3907d6eda41f0ff723d336125a1ad4349112cd4d48f693859980314d5b9da31c",
+    "https://deno.land/std@0.224.0/path/posix/resolve.ts": "08b699cfeee10cb6857ccab38fa4b2ec703b0ea33e8e69964f29d02a2d5257cf",
+    "https://deno.land/std@0.224.0/path/posix/to_file_url.ts": "7aa752ba66a35049e0e4a4be5a0a31ac6b645257d2e031142abb1854de250aaf",
+    "https://deno.land/std@0.224.0/path/posix/to_namespaced_path.ts": "28b216b3c76f892a4dca9734ff1cc0045d135532bfd9c435ae4858bfa5a2ebf0",
+    "https://deno.land/std@0.224.0/path/relative.ts": "ab739d727180ed8727e34ed71d976912461d98e2b76de3d3de834c1066667add",
+    "https://deno.land/std@0.224.0/path/resolve.ts": "a6f977bdb4272e79d8d0ed4333e3d71367cc3926acf15ac271f1d059c8494d8d",
+    "https://deno.land/std@0.224.0/path/to_file_url.ts": "88f049b769bce411e2d2db5bd9e6fd9a185a5fbd6b9f5ad8f52bef517c4ece1b",
+    "https://deno.land/std@0.224.0/path/to_namespaced_path.ts": "b706a4103b104cfadc09600a5f838c2ba94dbcdb642344557122dda444526e40",
+    "https://deno.land/std@0.224.0/path/windows/_util.ts": "d5f47363e5293fced22c984550d5e70e98e266cc3f31769e1710511803d04808",
+    "https://deno.land/std@0.224.0/path/windows/basename.ts": "6bbc57bac9df2cec43288c8c5334919418d784243a00bc10de67d392ab36d660",
+    "https://deno.land/std@0.224.0/path/windows/common.ts": "26f60ccc8b2cac3e1613000c23ac5a7d392715d479e5be413473a37903a2b5d4",
+    "https://deno.land/std@0.224.0/path/windows/constants.ts": "5afaac0a1f67b68b0a380a4ef391bf59feb55856aa8c60dfc01bd3b6abb813f5",
+    "https://deno.land/std@0.224.0/path/windows/dirname.ts": "33e421be5a5558a1346a48e74c330b8e560be7424ed7684ea03c12c21b627bc9",
+    "https://deno.land/std@0.224.0/path/windows/extname.ts": "165a61b00d781257fda1e9606a48c78b06815385e7d703232548dbfc95346bef",
+    "https://deno.land/std@0.224.0/path/windows/format.ts": "bbb5ecf379305b472b1082cd2fdc010e44a0020030414974d6029be9ad52aeb6",
+    "https://deno.land/std@0.224.0/path/windows/from_file_url.ts": "ced2d587b6dff18f963f269d745c4a599cf82b0c4007356bd957cb4cb52efc01",
+    "https://deno.land/std@0.224.0/path/windows/glob_to_regexp.ts": "e45f1f89bf3fc36f94ab7b3b9d0026729829fabc486c77f414caebef3b7304f8",
+    "https://deno.land/std@0.224.0/path/windows/is_absolute.ts": "4a8f6853f8598cf91a835f41abed42112cebab09478b072e4beb00ec81f8ca8a",
+    "https://deno.land/std@0.224.0/path/windows/is_glob.ts": "8a8b08c08bf731acf2c1232218f1f45a11131bc01de81e5f803450a5914434b9",
+    "https://deno.land/std@0.224.0/path/windows/join.ts": "8d03530ab89195185103b7da9dfc6327af13eabdcd44c7c63e42e27808f50ecf",
+    "https://deno.land/std@0.224.0/path/windows/join_globs.ts": "a9475b44645feddceb484ee0498e456f4add112e181cb94042cdc6d47d1cdd25",
+    "https://deno.land/std@0.224.0/path/windows/mod.ts": "2301fc1c54a28b349e20656f68a85f75befa0ee9b6cd75bfac3da5aca9c3f604",
+    "https://deno.land/std@0.224.0/path/windows/normalize.ts": "78126170ab917f0ca355a9af9e65ad6bfa5be14d574c5fb09bb1920f52577780",
+    "https://deno.land/std@0.224.0/path/windows/normalize_glob.ts": "9c87a829b6c0f445d03b3ecadc14492e2864c3ebb966f4cea41e98326e4435c6",
+    "https://deno.land/std@0.224.0/path/windows/parse.ts": "08804327b0484d18ab4d6781742bf374976de662f8642e62a67e93346e759707",
+    "https://deno.land/std@0.224.0/path/windows/relative.ts": "3e1abc7977ee6cc0db2730d1f9cb38be87b0ce4806759d271a70e4997fc638d7",
+    "https://deno.land/std@0.224.0/path/windows/resolve.ts": "8dae1dadfed9d46ff46cc337c9525c0c7d959fb400a6308f34595c45bdca1972",
+    "https://deno.land/std@0.224.0/path/windows/to_file_url.ts": "40e560ee4854fe5a3d4d12976cef2f4e8914125c81b11f1108e127934ced502e",
+    "https://deno.land/std@0.224.0/path/windows/to_namespaced_path.ts": "4ffa4fb6fae321448d5fe810b3ca741d84df4d7897e61ee29be961a6aac89a4c",
+    "https://deno.land/std@0.224.0/testing/mock.ts": "a963181c2860b6ba3eb60e08b62c164d33cf5da7cd445893499b2efda20074db",
     "https://deno.land/x/imagemagick_deno@0.0.14/mod.ts": "6b58c767d2308488597c3660e7ff399ede244198d7903900fa43a49cf93c7796",
     "https://deno.land/x/imagemagick_deno@0.0.14/src/alpha-option.ts": "749a9f3309e491ec09a1d6bc50ce95d9733887d9f57c6863c4ff1c7e9610227b",
     "https://deno.land/x/imagemagick_deno@0.0.14/src/auto-threshold-method.ts": "bb08a00046137e441930e56190b6db10c5fe657cb0a6142cd565a40b1c4250a2",
@@ -317,9 +417,6 @@
   },
   "workspace": {
     "dependencies": [
-      "jsr:@std/cli@^1.0.27",
-      "jsr:@std/fs@^1.0.22",
-      "jsr:@std/path@^1.1.4",
       "npm:sharp@~0.34.5"
     ]
   }
diff --git a/main.test.ts b/main.test.ts
new file mode 100644
index 0000000..89fdca3
--- /dev/null
+++ b/main.test.ts
@@ -0,0 +1,186 @@
+import {
+  assertEquals,
+  assertRejects,
+  assertStringIncludes,
+} from "https://deno.land/std@0.224.0/assert/mod.ts";
+import { stub } from "https://deno.land/std@0.224.0/testing/mock.ts";
+import { help, list, generate, main } from "./main.ts";
+
+Deno.test("help function - displays usage information", () => {
+  const logs: string[] = [];
+  const consoleLogStub = stub(console, "log", (...args: any[]) => {
+    logs.push(args.map(String).join(" "));
+  });
+  const consoleTableStub = stub(console, "table", () => {});
+  const consoleInfoStub = stub(console, "info", (...args: any[]) => {
+    logs.push(args.map(String).join(" "));
+  });
+
+  try {
+    help();
+
+    const allOutput = logs.join(" ");
+    assertStringIncludes(allOutput, "Usage: tile-maker");
+    assertStringIncludes(allOutput, "Commands:");
+    assertStringIncludes(allOutput, "generate");
+  } finally {
+    consoleLogStub.restore();
+    consoleTableStub.restore();
+    consoleInfoStub.restore();
+  }
+});
+
+Deno.test("list function - displays available rational angles", () => {
+  const logs: string[] = [];
+  const consoleLogStub = stub(console, "log", (...args: any[]) => {
+    logs.push(args.map(String).join(" "));
+  });
+  const consoleTableStub = stub(console, "table", () => {});
+
+  try {
+    list();
+
+    const allOutput = logs.join(" ");
+    assertStringIncludes(allOutput, "Available Rational Angles");
+  } finally {
+    consoleLogStub.restore();
+    consoleTableStub.restore();
+  }
+});
+
+Deno.test("generate function - throws error when input is missing", async () => {
+  await assertRejects(
+    async () => {
+      await generate({});
+    },
+    Error,
+    "Input file is required for generation",
+  );
+});
+
+Deno.test("generate function - throws error when input file doesn't exist", async () => {
+  await assertRejects(
+    async () => {
+      await generate({ input: "nonexistent-file.png" });
+    },
+    Error,
+    "Input file not found",
+  );
+});
+
+Deno.test("generate function - validates angle option range", async () => {
+  // Create a simple test image in a temp file
+  const testImagePath = await Deno.makeTempFile({ suffix: ".png" });
+  const pngData = new Uint8Array([
+    137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 1,
+    0, 0, 0, 1, 8, 2, 0, 0, 0, 144, 119, 83, 222, 0, 0, 0, 12, 73, 68, 65, 84,
+    8, 215, 99, 248, 207, 192, 0, 0, 3, 1, 1, 0, 24, 221, 141, 176, 0, 0, 0, 0,
+    73, 69, 78, 68, 174, 66, 96, 130,
+  ]);
+  await Deno.writeFile(testImagePath, pngData);
+
+  try {
+    await assertRejects(
+      async () => {
+        await generate({ input: testImagePath, angleOption: 999 });
+      },
+      Error,
+      "Invalid angle index",
+    );
+  } finally {
+    try {
+      await Deno.remove(testImagePath);
+    } catch {
+      // ignore
+    }
+  }
+});
+
+Deno.test("main function - handles help command", async () => {
+  const logs: string[] = [];
+  const consoleLogStub = stub(console, "log", (...args: any[]) => {
+    logs.push(args.map(String).join(" "));
+  });
+  const consoleTableStub = stub(console, "table", () => {});
+  const consoleInfoStub = stub(console, "info", (...args: any[]) => {
+    logs.push(args.map(String).join(" "));
+  });
+
+  try {
+    await main(["help"]);
+
+    const allOutput = logs.join(" ");
+    assertStringIncludes(allOutput, "Usage: tile-maker");
+  } finally {
+    consoleLogStub.restore();
+    consoleTableStub.restore();
+    consoleInfoStub.restore();
+  }
+});
+
+Deno.test("main function - handles list command", async () => {
+  const logs: string[] = [];
+  const consoleLogStub = stub(console, "log", (...args: any[]) => {
+    logs.push(args.map(String).join(" "));
+  });
+  const consoleTableStub = stub(console, "table", () => {});
+
+  try {
+    await main(["list"]);
+
+    const allOutput = logs.join(" ");
+    assertStringIncludes(allOutput, "Available Rational Angles");
+  } finally {
+    consoleLogStub.restore();
+    consoleTableStub.restore();
+  }
+});
+
+Deno.test("main function - handles version command", async () => {
+  const logs: string[] = [];
+  const consoleLogStub = stub(console, "log", (...args: any[]) => {
+    logs.push(args.map(String).join(" "));
+  });
+
+  try {
+    await main(["version"]);
+
+    const allOutput = logs.join(" ");
+    assertStringIncludes(allOutput, "Version");
+  } finally {
+    consoleLogStub.restore();
+  }
+});
+
+Deno.test("main function - throws error for unknown command", async () => {
+  await assertRejects(
+    async () => {
+      await main(["unknown-command"]);
+    },
+    Error,
+    "Unknown command: unknown-command",
+  );
+});
+
+Deno.test("main function - defaults to help when no command provided", async () => {
+  const logs: string[] = [];
+  const consoleLogStub = stub(console, "log", (...args: any[]) => {
+    logs.push(args.map(String).join(" "));
+  });
+  const consoleTableStub = stub(console, "table", () => {});
+  const consoleInfoStub = stub(console, "info", (...args: any[]) => {
+    logs.push(args.map(String).join(" "));
+  });
+
+  try {
+    await main([]);
+
+    const allOutput = logs.join(" ");
+    assertStringIncludes(allOutput, "Usage: tile-maker");
+  } finally {
+    consoleLogStub.restore();
+    consoleTableStub.restore();
+    consoleInfoStub.restore();
+  }
+});
+
diff --git a/main.ts b/main.ts
index 7815a2a..e4e5679 100644
--- a/main.ts
+++ b/main.ts
@@ -1,6 +1,6 @@
-import { parseArgs } from "@std/cli/parse-args";
+import { parseArgs } from "@std/cli";
 import { relative } from "@std/path";
-import { existsSync } from "@std/fs/exists";
+import { existsSync } from "@std/fs";
 
 import {
   findClosestRationalAngle,
@@ -13,30 +13,7 @@ import {
   GenerateTileOptions,
 } from "./src/lib.ts";
 
-const args = parseArgs(Deno.args, {
-  alias: {
-    angleOption: "a",
-    degrees: "d",
-    output: "o",
-    maxValidSize: "s",
-    allowLargeBuffers: "l",
-    quality: "q",
-    tileMargin: "m",
-    verbose: "v",
-  },
-  string: ["output"],
-  default: {
-    angleOption: 0,
-    maxValidSize: 2000,
-    allowLargeBuffers: false,
-    quality: 90,
-    tileMargin: 1,
-  },
-});
-
-if (args.verbose) console.log(args);
-
-function help() {
+export function help() {
   const commandList = {
     help: { description: "Display this help message" },
     list: { description: "List available rational angles" },
@@ -110,7 +87,7 @@ function help() {
 `);
 }
 
-function list() {
+export function list() {
   console.log("Available Rational Angles:");
   const tableData = RATIONAL_ANGLES.map((ra) => ({
     Label: ra.label,
@@ -132,7 +109,7 @@ export interface GenerateOptions {
   input?: string;
 }
 
-async function generate({
+export async function generate({
   angleOption = 0,
   degrees,
   output,
@@ -167,13 +144,13 @@ async function generate({
 
   // Calculate tile dimensions
   const metadata = await getImageProperties(inputPath);
-  if (args.verbose) console.log("Input image metadata: ", metadata);
+  if (verbose) console.log("Input image metadata: ", metadata);
   const tileDims = calculateTileDimensions(
     metadata.width,
     metadata.height,
     rationalAngle,
   );
-  if (args.verbose) console.log("Selected angle detail: ", rationalAngle);
+  if (verbose) console.log("Selected angle detail: ", rationalAngle);
   console.log(
     `Calculated tile dimensions: ${tileDims.width}x${tileDims.height}px`,
   );
@@ -214,7 +191,30 @@ Suggested fix: choose a different rational angle or increase the maximum valid s
   console.log(`Output saved to: ${outputPath}`);
 }
 
-async function main() {
+export async function main(providedArgs?: string[]) {
+  const args = parseArgs(providedArgs ?? Deno.args, {
+    alias: {
+      angleOption: "a",
+      degrees: "d",
+      output: "o",
+      maxValidSize: "s",
+      allowLargeBuffers: "l",
+      quality: "q",
+      tileMargin: "m",
+      verbose: "v",
+    },
+    string: ["output"],
+    default: {
+      angleOption: 0,
+      maxValidSize: 2000,
+      allowLargeBuffers: false,
+      quality: 90,
+      tileMargin: 1,
+    },
+  });
+
+  if (args.verbose) console.log(args);
+
   type Command = "help" | "list" | "generate" | "version";
   const command = (args._[0] ?? "help") as Command;
   switch (command) {
@@ -235,15 +235,18 @@ async function main() {
   }
 }
 
-try {
-  await main();
-} catch (error) {
-  if (error instanceof Error) {
-    if (error.message == "Input image exceeds pixel limit")
-      console.log(`Error: ${error.message}. Try setting the -l flag.`);
-    else console.error(`Error: ${error.message}`);
-  } else {
-    console.error(error);
+// Only run main if this is the main module
+if (import.meta.main) {
+  try {
+    await main();
+  } catch (error) {
+    if (error instanceof Error) {
+      if (error.message == "Input image exceeds pixel limit")
+        console.log(`Error: ${error.message}. Try setting the -l flag.`);
+      else console.error(`Error: ${error.message}`);
+    } else {
+      console.error(error);
+    }
+    Deno.exit(1);
   }
-  Deno.exit(1);
 }